Hanselminutes show #112 brings together people from xUnit.Net, NUnit, an MBUnit to discuss unit testing frameworks.  The whole show is worth listening to, but they especially mentioned running tests in parallel, which of course I've done some work on:

http://www.damonpayne.com/2008/05/09/ConcurrentUnitTestingWithXUnitNet0.aspx

http://www.damonpayne.com/2008/05/09/ConcurrentUnitTestingWithXUnitNet1.aspx

The other thing thing mention is the other potential intersection of Unit Testing and Concurrency: testing for thread deadlocks, etc.  I have been working for a few weeks on an article and some semantics (no working code this time due to the scope) that deal with exactly this problem space.  I should have it published this week.