We did not switch to Subversion because the people who develop Subversion are not sympathetic to the ideas of the free software movement. That is a sufficient reason, given that CVS works fine.
See the full thread here, and don't miss Karl Fogel's response as well as Jim Blandy's response (Karl and Jim are two of the founders of Subversion).
As a Subversion developer and an advocate of both open source and free software, reading this kind of crap from Richard makes my blood boil. More importantly perhaps, it makes me want to remove the words "free software" from my vocabulary.
Richard, if you really want to help Free Software, you might want to leaf through a copy of "How to Win Friends and Influence People", because you sure aren't winning any friends right now—in fact, you're in danger of losing the ones you've had for years.