You get all this honking and hoopla and what not, but nobody seems to think about the big Silverlight 4 Question:
Can I install Visual Studio 2010 Beta 2, Silverlight 4 Tools, WCF RIA Services, The November 2009 SIlverlight Toolkit, and Blend 4 Trial on the same machine that I have Visual Studio 2008, Siverlight 3, SIlverlight 3 Toolkit, Blend 3 and so on – and will they co-exist peacefully on the same machine?
Answer: Yes! All you may need to do is uninstall your previous RIA Services Preview.
Everything else will “just work”. I just did it and tested it all out.
Disclaimer: No animals were harmed in the creation of the UnBlog post. Your mileage may vary.
Oh, and one final note: If you are going to install WCF RIA Services with Visual Studio 2010, you will no longer be able to use RIA services with Visual Studio 2008. They don't install "side -by-side".