Oh goodness me! Can't BELIEVE we didn't have a KANK thread... sigh... we are so behind guys! 
I'd like to start off the discussion by posting this HILARIOUS (I mean HILARIOUS!!) blog/post thing that I found via Google about the storyline of KANK...
Don't worry, it is just SPECULATION about the storyline of KANK... of course, some of it could turn out to be true... so there is a POSSIBLE SPOILER ALERT... but if you don't mind that you have GOT to read it!!
Hilarious, man...
Kabhi Alvida Na Kehna!
Now I love Karan Johar. I love all his movies - his movies make me hysterical; they are that bad. I sincerely believe He, along with Sooraj Barjatya and Aditya Chopra are triangularly reponsibile for irreversible effect of sacchirine melodramas thronging Bollywood. I’ve been eager to watch Kabhi Alvida Na Kehna, Karan Johar’s next offering ever since he’s announced the movie. I am secretly hoping that this is his Alvida to Bollywood forever, though the name doesnt sound so promising.
Now a few days back I heard that KANK is a remake of English movie… “Closer”. Hmmm… Closer - isnt that the movie about extra marital affairs between straight couples? (pssst… I also heard that Karan Johar’s next movie is “Kaha Main Kaha Tu” starring himself and SRK, and inspired by Brokeback Mountain…). Anyways, thats not quite the point of this post. The point of this is to find out what exactly is the story behind Kabhi Alvida Na Kehna!
Now Karan Johar always gets the who’s who and who’s who not of bollywood to act in his movies - for some god damn reasons everyone agrees too. Nonetheless, as I was doing nothing, I decided to look up KANK’s entry in IMDB to get some idea of story line of this movie. Quoted verbatim from IMDB, this is what is the story of KANK according to them:
Jai Varma (Shahrukh Khan) and Shalini Sharma (Rani Mukerji) are married to Sharmila Varma (Urmila Matondkar) and Mohinder Sharma (Amitabh Bachan) respectively. Jai and Sharmila also have a son. Jai and Shalini believe that they are content and happy in their relationships. Until they meet each other. What starts as banter grows into something extraordinary. Their love throws their families into a turmoil.
Interesting. The first line had me in splits:
“Jai Varma and Shalini Sharma are married to Sharmila Varma and Mohinder Sharma respectively.”
I couldnt really read this limerick of a sentence for a while: Jai Varma, Sharmila Sharma, Shalina Sharma, Mohinder Varma… wait thats Sharmila Sharma or Shalini Varma? no, its Shalini Varma and Shalimar.. no Sharlima Sharmila. I have no doubts in my mind that this is a movie about Extra marital affairs. After all who’s who is the big question even before the movie has been shot. Karan Johar couldnt have thought of more creative names could he?
Next:
“Jail and Shailini believe that they are content and happy in their relationships. Until they meet each other”.
& here I thought they were already married to each other!
Oops. No. They are not. Jai is married to Sharmila & Shalini is married to Mohinder You got confused yourself didnt you?
Now, such a story of course has had the die hard fans of KANK in conundrum - aakhir who belongs to whom? and more importantly contrary to everyone’s expectation, what is Urmila Matondkar doing in this movie?! Yes Yes, Urmila. So to find answers to such life changing questions, I decided to read through a thread on the story line of this movie. Now, this forum and its answers are filled with Karan Johar fans who have decided to go all out and leak the story of the movie… as if anyone cared. Nonetheless, now here are some interesting responses in the forum:
Rani is married to Amitabh in this movie? i thoguht she was his daughter. Also ABhishek is Amitabh’s son in this movie too (like in “Sarkar”), so that means Abhishek is Rani’s son?
Hmm… I forgot about the son in the story in the Varma Sharma tangle completely. Who’s Rani? - Sharmila or Shalini? Go figure 
It’s wrong. Srk is not married to Urmie. Srk and Preity are lovers in the movie. They are opposite each other.
So SRK is not married to Urmila. This gets interesting. I thought Sharmila and Jai were married. Also Preity Zinta enters the story. Who is Urmila? - Shalini? Sharmila? If SRK and Preity are paired against each other, would that mean, Preity is Sharmila, Mohinder AmitabhBachchan Sharma’s wife? if so, Abhishek if Preity’s son? And Rani is Shalini?
No. Rani is not shalini either. I digged further…
The story-line seems very weird.
No SRK is paired opposite Rani.
Agreed. But I thought Preity ….
Further ahead…
Srk is paired with Rani and Preity…I guess. I read somewhere that he is currently linked with Preity [in the movie] but then there is a flashback how he was with Rani.
Ahhh. That solves the problem. Flashbacks to the rescue! Now we can piece the puzzle together. So SRK is paired with Preity and remembers Rani in flashback. Now Rani is Sharmila (or Shalini, who cares?), AB’s wife. SRK is paired with Rani in flashback meaning, AB was Mohinder back then, and AB and Rani were married. Assuming Preity is Shalini (or Sharmila, who cares?) and married to Mohinder, and Jai and Sharmila are to meet each other poses a problem. But that raises another question - did Jai meet Sharmila in flashback? No. Shalini is not married to Mohinder but Jai. And Sharmila was married to Mohinder - and Jai recalls Sharmila in flashback. And Sharmila and Mohinder have a son.
1 - Where is Urmila in all this?
2 - Exactly how old are these characters anyways if they have to time cross decades to meet each other?
So I digged on….
then who is Urmila?
Good question.
She is srk’s sis and/or maybe Arjun’s lover in the movie.
Urmila is SRK’s sis. Urmila is also Sharmila Sharma. Sharmila is married to Mohinder. Jai falls for Sharmila after they meet? INCEST?! What Karan Johar Upto. And moreover Arjun Rampal comes into picture - he’s in love with Sharmila. But Sharmila is contented with Mohinder until she meets her own brother Jai and falls for him!
No. This was getting a little out of hand….
Hmm … are you sure that SRK is paired with Rani? I remember Karan Johar saying that he got “Veer & Zaara” and “Bunty & Babli” for his movie. That kinda implies that SRK is paired with Preity and Abi is paired with Rani.
Abi is paired with Rani? Rani aka Sharmila Sharma? Abi is AB’s son and Sharmila is AB’s wife. So he is paired with OWN mother??????!
Good heavens…
ok, where the hell does Urmila fit then? I’m sure she’s more than just a supporting character since she’s equally as good as Rani!
That my friend was a very good question. I am guessing Urmila is also Sharmila and Rani is also Sharmila. And Preity is Shalini - that much seems clear at this point. Just when I thought I had it figured….
I really hope he’s paired opposite Preity. That’s also what I heard. That it’s SRK and Preity and Abhishek and Rani. But I guess we’ll just have to wait and see
Abhishek is paired with Rani. SRK is paired with Preity. So Rani = Sharmila and Preity = Shalini, which leaves SRK = Jai and Abhishek = Mohinder. Where did poor Amitabh Bachchan go?!! Uptil this point wasn’t he Mohinder, married to Sharmila? Also Sharmila and Mohinder have a son. Is Amitab Bachchan Abhishek Bachchan’s son? Karan Johar - you are simply marveolous!
I was about to give up at this point when I read these:
“SRK is married to Urmila, Rani is married to Amitabh, and then RANI and SRK fall in love!
I have no idea where Abishek and Preity come into it. “
Oops… Urmila is back.
Does anyone know where does Urmila fit into all this? I had no idea that she was also in the movie. I mean theer were never any announcements regarding her in the movie. There were always talks about how Arjun had replaced John in the movie but there were never any news about Urmila.
At this juncture I gave up when something important caught my eye, which tied the whole puzzle together finally!
one thing u r forgetting buddies …. SRK is doing double role …. JAI and MICHAEL 
…..
Ahhhh!! Thats it! Thats bloddy it! SRK in double role as Jai and Michael solves the bloddy puzzle! So here’s how it will be in the movie according to my predictions.
Michael is a former avatar of Jai. In his previous birth, he falls in love with Sharmila, aka Urmila. However, their love remains unfulfilled and Sharmila is forced to marry Arjun because Sharmila’s father has a heart attack on Kadva Chaut ki raath. However Sharmila commits suicide and promises Michael to return back to get back with him forever. Michael meanwhile marries another Shalini, aka Preity.
Sharmila takes a rebirth and is reborn as Rani. Rani grows into a lasso and marries Mohinder, 50 years older to her because he’s about to die and leave her a lot of wealth. Unfortunately he doesnt. And they produce a child. Abhishek Bachchan. On Abhishek’s fiance’s Kadva Chauth night, Sharmila remembers Michael again and her very purpose of her existance. Meanwhile, Michael and Shalini also have a child and he’s the double role Jai who’s come to fulfil the prophecy of Michael and Sharmila’s love story. Michael takes a promise from his Son Jai to fulfill his failed love and dies due to heart attack. So Jai and Sharmila rekindle their lost love; however, meanwhile Jai’s mom Shalini falls for Rani Sharmila’s son; But Mohinder Sharmila’s husband takes a fancy to Jai’s mom Preity aka Shalini.
In the end, Jai and Mohinder do mandvaani - aka, adjustment. Mohinder convinces Abhishek Bachchan to take a rebirth and fulfil his prophecy and he finally marries someone his age - Shalini. Sharmila though quite a mother to Jai now, doesnt care, because Jai likes ‘em old anyways. Hence everyone lives happily ever after, and Abhishek Bachchan gives a longing look to Shalini before committing suicide. His last words to her are “Kabhi Alvida Na Kehna!“. The same words Michael told Sharmila in previous birth.
The cycle of life is completed. Kabhi Alvida Na Kehna is completed!
Sigh - so simple! And here was I ransacking by brain to solve such a simple story. Pah!
I am terribly excited about this movie.
Source: http://www.suyogdeshpande.net/blog/2006/01/10/kabhi-alvida-na-kehna/
Give the guy a visit! 
END POSSIBLE SPECULATION/SPOILER/WHATEVER ALERT.
OK... so! I cannot wait for this film... especially to see the picturisation of the songs... although yes, I have seen the trailers... and, of course, to find out how much of that ramble turned out to be true! 
BTW... PLEASE PLEASE mark ALL spoilers and SPECULATIONS too... outta respect for other members who might not have wanted to know...