Some people keep their entire home directories in Subversion, which is clever but takes up quite a lot of space. For my own needs, I’ve always just kept any code (of course), my work documents and my book collection in Subversion, so I can check out and edit the parts I need on any machine.
Half a year ago I’ve also started checking in savegames, for Diablo 2, Sacred, Fallout 2 and the like. It’s very useful if you play the same games on multiple machines, you no longer have to remember to copy saves from one box to the other. Well, as long as you remember to commit.
The only unhappy bit is that most savegame formats are binary blobs, so you can’t actually diff things in a meaningful way 😉