When DragonFly was moving away from CVS, the votes were split pretty evenly between Git and Mercurial. DragonFly went to Git, but it’s apparently now possible to use Mercurial with a Git repository.
A running description of activity related to DragonFly BSD.
Btw, there is mercurial SoC project progressing which has a same goal. See http://permalink.gmane.org/gmane.comp.version-control.mercurial.devel/22883 for details.