Ruby’s Test::Unit library (which we use for Basecamp’s tests) creates a new instance of the test class for each test. Not only that, but it holds onto each of those instances, so if your test suite includes thousands of tests, then the test suite will have thousands of TestCase objects.
On the Java side, JUnit does exactly the same thing. However I usually see this manifest itself as out of memory errors rather than a time sink. Over the years I have gotten some VERY strange looks from clients when I null out instance variables in my tear down methods. Usually takes a couple of hours of explanation to gain some level of acceptance, if not understanding.