I used CVS for some years now and recently switched to Subversion. I was surprised that the commands for ci, co, etc. are identical to the cvs commands -- no re-learning:

$ cvs ci
[...]
$ svn ci
[...]
[download]

But, there are additional commands like svn mv. The only difference I noted (but I use SVN/CVS only as an "intelligent backup", no more advanced things) is the way you create a new repository, but there's an excellent quickstart guide (link lost). I couldn't imagine developing without using some kind of version control system -- it's much easier to use than cp/scp/tar/rsync :)