I had a confusing installation experience today. Trac was installed in /usr/local/lib/python2.4/site-packages/trac, and I checked out a version that I had hacked to use setuptools, and run "python setup.py develop" on. This added my checkout to the path, but after site-packages, so it wouldn't be loaded, even if I did require('trac'). Now, if I did setup.py develop -m it would actually work, because setuptools would fix up the path correctly.
I don't know the best resolution here. Maybe develop should check for conflicting installed packages?