Everybody experiencing this problem should also check the size of their project file. If it’s above 10-12Mb (easily achieved on docs with multiple versions), you need to slim things down and adopt a different workflow.
Break the project down first into Media/Edits, then further down into chapters/acts/interviews, whatever seems most logical. Also weed out redundant edits by archiving them, keeping the project with your main edit up to date and as lean as possible.
There’s no problem for FCP to have multiple projects open simultaneously, you can copy, cut and paste between them.
Also, make sure that you regularly save your projects using the “Save As…” dialogue, forcing the whole file to be re-written from the ground up on a regular basis. Apparently months of saving to the same file is a recipe for corruption, and simply backing up a buggy file is no insurance against losing your work.