The performance of my instance of VS2010 beta 2 was not well. Especially, start of debugging process for silverlight applications was not fast enough. Loading of symbols files (to enable debugging) was taking about two-three minutes. BTW, there are a lot of complains on performance in beta 2. The situation was the same for silverlight 3 and 4 applications.
The performance issue has been solved after installing MS Expression Blend Preview for .Net 4. The symbols loading time is almost the same as for VS2008.
I am absolutely sure, Microsoft will improve performance in the release.