While I was learning how to use Mercurial in order to contribute to the Mozilla platform, I became addicted to it, and with the migration tools now I have access to my repositories with full history on the go, without need of permanent connection to the CVS or SVN server. I can even do offline commits to my local copies.

I had not found a nice GUI for it yet, but being restricted to the command line is not a big reason to not use the powerful offline features. ummmm OpenJDK is stored on Mercurial, and Netbeans 6.1 finall will have support for it.