Congratulations to the Ruby language folks for converting their CVS repository over to Subversion (SVN). From what the "experts" tell me, it is not easy moving your developers over to another version control system. At least that's what was hinted when I asked the question, CVS or Subversion?
The difficulty of moving a project to a different version control system likely has just as much to do with cultural issues as it does with technical issues. To ask a developer to use a version control system when they never have used a version control system before is difficult enough. To ask a developer to spend a day or two to learn a new version control system over the one they're currently using is three times more difficult.
For the organization that I work for, we've settled on SVN. A lot of the developers in our field offices are used to programming alone, thus most of then have never used a version control system. I believe we'll find SVN is the right choice for the new projects we're starting up.