Perhaps I'm paranoid but if it's for a client we keep the export files as well. Mostly becasue there are several versions of design going to the client and they reponds to those files. What's on my desktop right now is (indeed) exported stuff for my own little side projects, some logo's I need to check, some completed and archived projects that I need to borrow from and a copy of some handy UI stuff I keep using for new designs.
But if my PC crashed right now, no projects would be harmed. And if I need a older version of something it's all on the server. If I accidentily delete an entire project I can get it back in 5 min.