Not only do I think we should support calling our tests via unittest, I think we should move in the direction of having regrtest be implemented via standard unittest hooks rather than the monster it currently is.  That will take quite a bit of effort, though :)

Given that we are in fact using unittest, I think it is much clearer to follow the standard unittest pattern and have tests that are supposed to be run marked by subclassing TestCase, rather than by being explicitly nominated in boilerplate at the bottom.  Certainly any new test files I write work that way (and I even explicitly use test discovery in test_email).