Just finished writing some test code for some shared utilities on my current project. The project is a BizTalk project so the utilities can be hit from multiple threads and from multiple boxes (with a shared database box). So I needed to test for these scenarios. The multiple threads was pretty easy, but I found this page to be very useful and thought I would pass it along.
I also attempted to simulate the multiple box scenario by creating multiple AppDomains (one domain per thread) and then hitting the utility from the separate domains. In figuring out how to do this I made use of this article by Eric Gunnerson. The tests all pass, which is good, but I'm not totally convinced that I'm really simulating things correctly.
Anyhow, both those links are good reads that I want to remember...