So, a while ago Martin von Löwis asked who would champion the migration to Mercurial, and I volunteered. He asked me to produce a PEP outlining which steps to take, which I've been working on. The PEP is numbered 385, and is just about ready for your review. I'd really welcome any sort of feedback or questions about Mercurial and surrounding tools relevant to the migration project (I'm happy to answer other questions as well, but maybe python-dev is not the appropriate forum for that -- instead, try mercurial@selenic.com and/or #mercurial on freenode).
http://www.python.org/dev/peps/pep-0385/
In particular, you may want to review (a) branches that you care about and whether they would be migrated under the current proposal, (b) non-release tags that you think are useful and (c) the author map (check if it has a correct email address for you and people you know).
Thanks to Antoine, Benjamin, Georg and Martin for early feedback.
Cheers,
Dirkjan