I use CVS at work and for personal projects (I even used it for many undergrad assignments). My main complaint is trouble doing the branching and merging (also deleting and renaming files erase all history of those files). Maybe I just haven't learned enough about how to use CVS. (I assure you I've read and googled and tried to figure it out though.)
One company I've worked with is currently considering subversion though they haven't switched over yet and I understand there is a fee to use it.