Google Code is shutting down, so Vim is finally moving to GitHub! You can find it at vim/vim.
I found this through the vim dev group. Given that almost every Vim script that I write about is hosted on GitHub, is seems clear that the community at large prefers GitHub. So why was Vim so slow to follow everyone else? Bram Moolenaar said the following on the vim dev mailing list:
This is not without disadvantages, since it means moving from Mercurial to git. Some may like this, some not. Will take some getting used to. I personally prefer the Mercurial commands, they are more obvious to use.
If you prefer Mercurial to Git then this is completely understandable, but for those of us who basically use GitHub 24/7 it's definitely convenient to have Vim hosted there as well. Sometimes you have to go with conventions rather than technically well reasoned preferences.