My main complaint with CVS is that it doesn’t support file renames (!!) without some kind of wacky hacks if you want to preserve the revision history of a renamed file. I find rename support to be essential when refactoring. I’m keeping a close eye on Subversion (still in alpha) which aims to address the shortcomings of CVS.[Otiose Cognitions]
I want subversion to succeed, trouble with something like source-control is that it has to be stable and reliable first and foremost – that’s its job. So overcoming the initial ‘new (and potentially buggy) stuff’ hurdle is that much harder. Attaining critical mass will be, erm, critical.