I experienced a hard lock-up of my Mac (running OS X 10.5.5 and IDEA 8.0.1) and when I restarted my copy of IDEA the project was very broken. The project now consists of only the library, and none of the project files are showing up. See below:
Additionally, if I close the project and then try to reopen it, when I nav through my directories to find the .ipr file, IDEA doesn't even show any files under the project directory, though they are all still there. (again, see image below:) If I launch the project by double-clicking the .ipr file directly, I can make it launch but with no files showing, again.
If I launch IDEA 7.0.4, the project still works just as it always had.