hg-git[1] lets hg interoperate with git repositories, which helps a bit with the network effect problem. I'm currently using hg-git for my projects and I am loving it because I much prefer the hg UI (both the command line and tortoiseHg) to git's UI.
I use this constantly --- I've been migrating all my projects to github. hg-git Just Works (almost; there are a few places where the git model doesn't match up with the hg model).
If you like hg, but want to exploit git's network effects, I strongly suggest checking it out.
[1] https://bitbucket.org/durin42/hg-git