IDEA 7 has a nifty feature called 'Shelve changes'. Some SCM systems have this -- it's the ability to take a set of changes and have the SCM 'forget' about them so you can do other work independent of them. You can then reintegrate them back in one fell swoop. The typical use case is to move aside changes for a big feature to implement one or more small features at the same time so you don't accidentally bring the 'big feature' changes in with the small ones.
(From what I understand this is built-in to most distributed SCM systems -- branches aren't the heavyweight things they are in Perforce, so every feature becomes its own branch and has its own changesets associated with it. Cool.)
Anyway, somehow IDEA lost track of a shelf I'd made a week or two ago -- I hit Alt-9 to see the changes, then Alt-RightArrow twice to the see the 'Shelf' tab, only to see there was no 'Shelf' tab. Shit! I tried to remember everything I did, and while it wasn't a huge amount it was an hour of work plus testing.
Before I started on that path I went to the directory where IDEA stores all of my stuff: ~/.IntelliJIdea70. Under config/shelf was a single file with the extension of .patch and the name I'd given the shelf. Sure enough, the tried-and-true patch format sat there, and after choosing 'Version Control | Apply patch...' my changes were brought back in. Awesome!
It would have been really easy for the folks at Jetbrains to create their own format for shelved changes, and to tightly couple the 'reintegrate shelf' functionality with the file itself, disallowing its use anywhere else. That they didn't shows, again, how much they know how developers work. The fact that I also could have applied them with the command-line patch tool is also great, and another argument for sticking with standard formats where possible.