pandas-svn mailing list?
Upstream repositories like `numpy` and `scipy` have a `numpy-svn` and `scipy-svn` mailing list that is used to avert users of commits / merges to the `master` branch.  You can find those lists <a href="http://www.scipy.org/scipylib/mailing-lists.html">here</a> here.  I personally find it useful to get such emails because it allows me to make sure that my PR branches don't fall too far behind the `master` branch.  I see no reason why the `pandas` repository wouldn't benefit from such an emailing list either.
