Mercurial has had git-like "lightweight branches"/bookmarks without the revision record of mercurial named branches for over 15 years.
There are good reasons to use the traditional branches though.
The topics[0] feature in the evolution extension is probably even closer to Git branches, since they are completely mutable and needn't be a permanent part of your repo. Bookmarks are just pointers to changesets, and although that's technically how Git branches work, it's not how they work in practice in Mercurial because of its focus on immutability (and because hg and git work differently).
