Even you divorced your American citizen spouse, you still have a chance to get approved for GC based on marriage, as long as you can prove your marriage is real and valid.
My personal timeline
Married in Dec, 2001
Get EAD in July, 2002
Interviewed in Jan,2003 and get Conditional GC, which expired in Jan. 2005
Divorce finalized in Sept, 2004
Filed I-751 in Nov. 2004
Received Notice of Action in Dec. 2004, and extension of my Conditional GC to Nov, 2005
Received interview letter for I-751 in July, 2005
I-751 Interview by myself in Aug, 2005
Two weeks later after interview, I received the permanent GC (10-year card) in mail(California service center). Hope this could be helpful for someone else, especially for those in unhappy marriage.