<p>My current project uses NUnit for unit tests and to drive UATs written with Selenium.  Developers normally run tests using ReSharper's test runner in VS.Net 2003 and our build box kicks them off via NAnt.</p>

<p>We would like to run the UAT tests in parallel so that we can take advantage of Selenium Grid/RCs so that they will be able to run much faster.</p>

<p>Does anyone have any thoughts on how this might be achieved? and/or best practices for testing Selenium tests against multiple browsers environments without writing duplicate tests automatically?</p>

<p>Thank you.</p>

There hasn't been a lot of work on this subject. I didn't find anything really relevent.
However, your point is well taken. Most machines nowadays have more cores and less powerful cores compared to powerful one core cpu.
So I did find something on a Microsoft blog. The technology is called PUnit and is made especially for testing multi-threaded environment.
It's as close as possible to what you requested that I could find :)
You can visit it the appropriate blog post right there:
http://blogs.microsoft.co.il/blogs/eyal/archive/2008/07/09/punit-parallel-unit-testing-in-making.aspx
Update: Link is not valid anymore. The project on CodePlex has been removed.
Update2: This is on the roadmap for NUnit 2.5.
Reference