Git is amazing but I take issue with GitHub. The point of Git is that it's a distributed and decentralized version control system and GitHub gets rid of the decentralized part of that. That is counter to what Git was designed for.
For people coming from client-server SCMs, I think Github is a really important transition step, and frankly, as an open source developer and consumer, it's really nice that there's a popular publish/find-stuff hub.
In fact, I think the blog post here reaches the wrong conclusion, in that everything he thought about using git is actually (still) true, but it is widely successful anyway because of other projects (mostly related directly to GitHub) which hide the complexity of git from the "9-5" developers.