Nobody talked about subversion in this thread, and I'm not sure why...
I haven't used it, only considered it for future projects after reading the docs. But the concept was to make a cvs replacement, with its advantages and without its hassles/disadvantages. Last time I checked, the apache project was seriously considering moving to subversion, so it can't be that bad. Oh, and the license is Apache/BSD, just for comparison with the bk/arch crossfire... ;-)
I also found a brief comparison of version control systems, for the decisionmakers:
http://better-scm.berlios.de/comparison/comparison.html
Fernando