Not sure if this is still a valid approach, but on a large Django site with a lot of unit tests, the cumulative setup/teardown/reset cycles was killing us. We found that setting each test to be wrapped with a transaction that was aborted on teardown, caused the per test cleanup to drop radically. We also kept a canned database for testing so that running the test suite didn't have a large startup penalty to populate the database with test fixtures. Keeping that ready db between runs also sped things up a lot for devs.
