I've used Mercurial more than Git, but GitHub looks so nice and polished that I wanted to see it in action.

So by way of experiment I forked Io, and fixed up some documentation typos. Today these were merged back: 1882b78. How exciting. I love the network graph:

which is explained here and is html5 canvas goodness.

Later I was able to push a fix to a mailing list issue, providing a convenient diff.

Likes so far: Ah, the freedom of DVCS and open source: not having to ask permission to fork. Checkin early, checkin often. Cloning trees locally. The three-way "pull upstream, push origin" model. Pretty diff viewer built-in. And Github does make it easy.

Dislikes: Git's complexity will take some getting used to. The GitHub Issues lists look a little too simple; I wonder if it is sufficient in practice.