I installed the February CTP edition of Visual C# Express a couple of days ago to build and test XML-RPC.NET with the latest Whidbey release. My unit tests failed in two places: proxy generation using System.Reflection.Emit failed because TypeBuilder.CreateType could not create the proxy class due to an "inaccessible interface" error, and Activator.Create instance failed to successfully create a multi-dimension array. When I get some time I'll investigate these problems further, though according to several reports beta 2 is due at the end of this month and so it may be worth wating until then to see if the bugs have already been fixed.
For a piece of software which has been under development for so long, I was not terribly impressed by this version of Visual Studio. When debugging, various windows, e.g. call stack and locals, would appear each time even though I had closed them on the previous run, and in general the IDE became extremely sluggish after using it for a while. Hopefully this is caused by huge amounts of diagnostic code which will be removed by the time we get to beta 2