[JoshTriplett]

Version control has strong network effects. If you use a particular VCS, it's in your best interests for every other project to use that VCS too. And if most projects are using a particular VCS, it's likely in your best interests to use that VCS too, whether you think it's technically the best or not.

That said, I'd never call mercurial outdated. If I saw it on a resume or someone mentioned it when asked what version control systems they'd used, I'd consider it a major positive, much more so than if I only see CVS, which in turn is better than seeing no version control at all or having someone give a blank look when asked what version control systems they've used.

And if someone says they've used both mercurial and git, that's the perfect opportunity to ask them to compare the two and mention what they like and don't like about each. If you've only ever used one, you don't necessarily have the basis on which to make a good comparison.

I've used both mercurial and git (as well as RCS, CVS, SVN, tla/baz, and bzr), and I can spell out exactly why I prefer git over each of them.