I made all of the changes required to get units running in Python 3.3. I described what was necessary in more detail in the commit messages. I'm confident that the changes in 2492a97 won't be an issue, but the changes in fdac22c could use your review.
I also added a Tox config file so the test suite can be run on multiple Python versions. Just make sure you have them installed as python2.5, python2.6, python2.7 and python3.3 and run 'tox'. To just run the tests in Python 3 you can run 'tox -e py33'.