I’ve posted an article on my MSDN blog about strategies and considerations when composing your test cases.  If you’re familiar with Test Case Authoring in MTLM (Ryan Vogrinec and David R. Williamson both have helpful posts on the subject), you can read more about the possibilities and tradeoffs in Test Case factoring at the following link:

http://blogs.msdn.com/joemu/archive/2009/11/16/zen-and-the-art-of-test-case-composition.aspx

Enjoy,

Joe Allan Muharsky