Subgit and Subhg are interesting.

http://rustyklophaus.com/articles/20100124-SubmodulesAndSubr...

Just use Mercurial for random private commits, send the Git people your changesets every so often:

    $ git init && git add . && git commit -m "Initial commit" && git remote add origin git@github.com:acct/repo.git && git push -u origin master
    $ subgit setup
    $ hg init

hginit.com <-- great resource

http://code.google.com/p/support/wiki/DVCSAnalysis

In Google's own words: "In terms of implementation effort, Mercurial has a clear advantage due to its efficient HTTP transport protocol.

In terms of features, Git is more powerful, but this tends to be offset by it being more complicated to use."