After installing the MAY CTP of LINQ, the refactoring menus in VS2005 stopped working. I use that a lot, so I either had to find a way to fix it or uninstall LINQ! I found a post on the MSDN forums that solves the problem. There is a registry entry you must change along with running a few commands from the command line. I have zipped up two files that will make the process a little easier.
There is a reg file and a cmd file contained in the zip file. You may need to edit the contents if you have installed Visual Studio somewhere besides the default location.