It's fun rereading this thread and seeing how everyones theories developed. I'm surprised I never posted on it; I remember reading some of it before.
The last couple of episodes of Lost (Season 2) convinced me that I wasn't remembering enough, so I got the DVD's. There's some interesting bits about how the series could have been.
As mentioned before, Jack was supposed to die in the pilot. Originally, Michel Keaton was up for the part, but he didn't want a regular role.
Kate was originally the lead character. She wasn't going to be a fugitive, and she was going to have a husband in the tail section. (Maybe that's what inspired her short marriage mentioned during the drinnking game.)
The actress playing Sun originally tried out for Kate, but when the creators found out she had a strong movie career in Korea, they came up with the Sun character just for her.
Sawyer started out as a white collar, metrosexual con artist from Pitsburg with a somewhat less traumatic childhood. The actors playing Jack, Charlie and Hurley all auditioned for the part. Jorge Garcia's audtition was an interesting scene where Kate found out that Sawyer had plundered he husband's luggage.
Claire was originaly a surrogate mother for her best friend.
It's a good set; I'm glad I got it.