Clearcase does rock, if you have an admin and the money :)
And, well, the GUI tools (who needs GUI tools) don't work so well and the MVFS kernel module only supports about 3 crappy Linux distributions -- and old versions of those too (no Debian or FC, etc).
I'm a Linux guy. At home I usually don't do anything big enough to need an RCS, but I really should use one out of habit as I'd be more likely to get used to it and use it in places where Clearcase isn't.
IBM CMVC, now that was painful... CVS isn't that bad, I need to try SubVersion and ARCH at home on my Debian boxen. ARCH actually sounds cool from the Wiki page, but I have yet to see it in action.