During a Team System class I was teaching yesterday, one of the attendees asked a question that I couldn't answer. Although that isn't the first time, that same attendee proceeded to go home and figure out the answer and send it to me. For his efforts, I could do no less than repeating it here...
Q: Where are the test lists stored for test manger?
A: In the SolutionName.vsmdi file. This file is stored at the solution level and is in source control, which is how different users can get access to the same test lists for the same VS 2005 test projects.
Thank you to Durant Rodrigue for figuring this out and sharing.
(Updated shortly after initial post - fixed typo in file extension)