This almost slipped out of my sight. Visual Studio 2010 adds an option to execute unit tests in parallel. Probably it would be obvious but let me emphasis that all multithreading issues could arise and let tests fails in such case. So all tests must be thread safe and tested code as well…
The option to enable this is very hidden 
It is not exposed via VS GUI but in .testsettings file instead. It has to be edited in XML editor and add to <Execution> parallelTestCount attribute greater than 1(e.g. parallelTestCount=”4”)
Hope this helps