I just saved a file I was working on and Flash CS5 crashed on me as it was saving and now the file is corrupt and won't open (because of our obsolete file system).
So I recommend OS X users to use Time Machine so you always have a backup of the file being made as you work.
I understand that this post is mainly a reccomendation, but on another note; Is the entire file corrupted? I am on a Mac running Snow Leopard, and with some files I corrupted intentionally to test a problem like this, I was able to collect a good amount of the contents. Exam the contents within the folder/file/document, normally you can pull out some content that is unharmed.
Just don't want to see you do more work then you have to