Forum OpenACS Q&A: Response to Bitkeeper experiences?
Switching from CVS to Perforce was a bit challenging with the new terminology, commands, and infrastructure, but it wasn't too bad. In fact, one of the developers wrote a CVS to Perforce transistion guide - http://developer.arsdigita.com/acs-java/resources/perforce/cvs-perforce-transition.html.
For those of you worried about the license cost, note that Perforce licenses are free if the server is used for development of open source software. See http://perforce.com/perforce/price.html for more info.