Excellent point! I just wanted to add this one - for Windows Tortoise is a pace further than WinCVS which to me is just a bug ridden crap ...most of the commands lack their GUI options too and using command line in specific cases is jus too tedious ... They've had also issues with SP2 recently. Ain't of the same opinion about the gnu tool ... to me it's just perfect ...although VSS is used by most developers/doc developers these days for checkins/checkouts ....
Here you can find the CVS docs ....
http://www.gnu.org/home.html