I'm writing to let you know that we have outgrown our homegrown mercurial serving (as some of you may have noticed with the installation errors) and we have moved the yt source code to BitBucket. Here are the three takeaways:
The new source code location is the same as the old source code location: http://hg.enzotools.org/ . The username on BitBucket is "yt_analysis". The DNS might take a few hours to get circulated around, so if it doesn't work just now, it will by tonight or tomorrow.
To contribute changes you can go here: http://hg.enzotools.org/yt/fork to get your own version of the yt repository, where you can make changes and commit, and even notify the main repo when your changes are ready to push back upstream. We're very excited that this will enable much greater participation, and I hope that this will lower the barrier to entry for developing yt! I'm rewriting the developer guide now, but the short answer to how to make changes has gotten a lot shorter: just fork the repository and issue a "pull request" when you're ready to contribute back upstream.
Let us know if this causes any unforeseen problems, and please feel encouraged to fork and contribute!