Aside from all the other technical bits, one killer feature for my company is TortoiseHG (http://tortoisehg.bitbucket.org/). Unlike a number of the other Tortoise-* projects (which don't seem related actually), TortoiseHG is a really great cross-platform gui, written in python & qt -- runs just about everywhere, and makes working with mercurial uniformly easy.

The fact that instead of "hg ci" I can type "thg ci" and get a commit window with cherry-picking and meld integration right off the bat is really powerful. I've not seen any good git guis that come close to it's featureset.