The power of github
A lot has already been said about github, but I guess it can't harm if I make a list of my preferred features:
Dashboard (need to be logged in to see): this is your personal start location. It contains many useful links and other automatically generated information, such as news from people you track ("follow"). It is the most prominent feature regarding the user-centered approach of github, and having it just feels so right to me.
Comments on change sets: Each line of code in a change set can be commented on. Don't fall for the comment box at the bottom, it's only a fallback if your browser isn't web2.0-ready. Click on the markers to the very left instead, and you get a pop-up window together with a preview feature for your comment (much better, isn't it?). Of course those comments tend to become less useful when change sets grow too large, so commit often (you should do that anyway). Also, if someone who is tracked by you ("followed") makes a comment it will automagically appear on your dashboard.
Diff view: An expedient diff highlighting makes it easy to track changes down to the letter. A red/dark red background indicates removed lines/characters, while a green/dark green background indicates the opposite. This is far better to read than the simple +/- in front of lines. One could argue about the use of red, instead of purple (in terms of a11y).
Source tree browser: a must-have in any [D]VCS web front-end, but what stands out is the simple hack that allows to mark lines (try SHIFT/CTRL to select multiple lines). The URL is modified to represent this selection (#L1-L4 would mean line 1-4 are selected), which comes in handy when discussing your code with other people.
Automated configuration of remote repositories: If you find it too hard to set up your own remote repositories with git (or perhaps you simply lack shell access to the remote server) then github will gladly help you out. Register an account, if you haven't already, upload your public SSH key and create as many (public, or private if you upgrade your account) remote repositories as you want. Others can instantly clone from such a repository - you do not have to wait for a BofH to enable it!
Fork queues: Simply put, this is github's killer feature. It makes collaboration sweet as apple pie. Once the number of project contributers grows beyond one you will find this feature invaluable to track their change sets. If a repository is forked, github will keep track of the association and report any change set that is committed to such a fork back to you. Even better, you can cherry-pick from their forks and merge their patches into your project.
I wish I could comment on lines of source code too (in revisions) without finding the commit that added or changed that line.
In fact, I wish that this commenting was a feature of git itself.
Michael, yes, I think that you summarised the good points of Github perfectly. For someone new to version control (like me) it makes the whole process a lot easier, and doesn't get in the way for experienced users.