Earlier this week, I bought a license for SourceGear Vault - a tool for keeping track of changes to source files. I'd previously tried Microsoft's SourceSafe, but struggled a little. The common theme among users (that post to newsgroups or Wikis) is that SourceSafe is fine for a single user or single machine environment, but starts getting hairy for multiple users.
First impressions are good. The admin tool has a terrible user interface (a tabbed dialog with the tabs at the bottom, but facing up??) but isn't too bad to use; the main GUI client looks and works a lot like SourceSafe.
I got through 30 revisions of my repository today; I think I need to learn a bit of restraint with checkins. I did have a slight problem with Obliterating branches I decided afterwards wanted to get rid of - the solution is of course "don't do that!"
When working on my final year project, SourceSafe was quite handy - I ended up following a number of false paths, and it was easy to roll back to a baseline without those paths.