Eric D's post Subversion on the PC just reminded me howintegral TortoiseSVN has become in our team.
I introduced SVN/Tortoise SVN to our team earlier this year, and I have to say it's been fantastic - saved our butts on numerous occasions, especially when we've three simultaneous branches of development on the same system, plus live bug-fixes.
The only issues I have with it are
1) merging branches can be very counter-intuitive - I've done it numerous times, and I *still* need the help docs open while I fill in the form
2) it's a bit too easy to to get a working copy into a state where you can't commit, can't update, and can't clean up. The only thing you can do in that case is checkout an entirely new copy, manually port across your revisions, and junk the old copy.
3) terminology - if the "Update" and "Commit" menu options were just a bit more expansive (e.g. something like "Update this copy from repository" and "Check changes back in") it would save a fair amount of confusion amongst the less-technical team members.
All in all though, it is a great piece of software - if you haven't tried version control, or if you've only used something like Visual Source Safe or WinCVS, I thoroughly recommend giving Subversion + TortoiseSVN a try.