I'm on a development team of 1, so source control isn't a huge or pressing issue for me. The biggest advantages of having source control is for rolling back to earlier versions, and using a diff tool to see what I've changed. It also means I follow some better practices than just developing away, heedless of key files I might overwrite, or changes I might make that break a system.
About a year ago I set up CVS, which worked pretty well. It took a lot of fiddling to get working just right, but when I figured out the securities and settings, Visual Studio.NET played along pretty nicely with it (using Jalindi Igloo). I would give either of those two products a hearty recomendation to anyone interested in CVS source control on Windows.
Then the Windows 2000 server I had CVS working on started playing up - it had very little memory, I was asking a lot of it, and I had a whole bunch of demo and beta software on it that meant it needed a rebuild. Eventually we got a new server instead of rebuilding the old one, and eventually that new server got repaved after a power blackout (long story).
So now I feel I'm back at square one. I've downloaded Vault and Subversion (thanks to Steve Eichert for an interesting & informative post on Subversion) and I'm poised, ready to pull the trigger and go with one of them. I'll have to try them both out, of course. Leaning towards Subversion as it's open source and that means that others can come on board without having to cough up dough for licenses. Alternatively, I've expressed interest in a project out of hours that uses Vault, so maybe getting to learn that would be good. Vault has the fact that it's a mature and supported product going in its favour.
Add to this the new Team System on the horizon, and it makes for a lot of source control options!