The MT 3.31 Plug-in Compatibility List
Elise Bauer, author of Learning Movable Type has published the PCL. (Do you remember the NT4.0 HCL? If it wasn't there, it wasn't going to work with NT.) I found this more recent and relevant document while doing some last minute research before doing upgrades this week. If you are upgrading your MT blog, you probably want to take a quick look to see if your favorite plug-ins are on the list.