I liked the idea of monotone, since it could work in places like Freenet, but then to build it you need to build Boost, which is, IMHO, a total piece of crap and couldn't build properly at all on my machine, regardless of what I did with their crappy "BJam" makefile-replacement shit.
Then you have Darcs, but it is written in Haskell (some obscure programing language), so you need ghc. And to install ghc on Mac OS X 10.2, you can't compile it, so you need to use darwinports to install it. I'll pass.
What remains is arch, a pretty low-level, UNIX-style Bitkeeper-like system. Really nice, but damn it's difficult to learn. It took me a day of learning to understand how you can "push" changes you did on your branch to the trunk server by email (it's by using the "tla delta" command, if you want to know).
After all, arch can be good if you have a hierarchical code development system, like what they do for the Linux kernel. To allow others to "pull" the code, you host your archive files in a WebDAV of sftp server. To push, upwards, either ask the maintainer(s) above you to "pull-and-merge" from your server, or compute the chanset yourself and send it by email.
Yep, you have to learn lots of concepts to use that... So if you only want to replace CVS at work, just use Subversion when it will hit 1.0 at the end of the month...
Let me rephrase that: in two weeks, subversion hits version 1.0, after 3.5 years of development and bug-testing! YES!