I highly recommend that you install the service pack if you are running into VB compiler performance issues with large projects. This service pack contains the fixes that was released as a hot fix described in the VB blog here.
When I first joined the VB team, the team was just starting to realize that the performance of the compiler did not scale out to very large projects. There were also other issues with scaling out in terms of number of errors in the solution, etc. As a result, there was a push to address these issues and make sure our customers understand that we feel their pain. A few co-workers of mine spent lots of time talking with customers, identifying their issues, and making the appropriate fixes. The result is SP1 which contains a number of fixes.
One of these days, I'll blog about the various improvements that we've made and show the underlying problem and solution that we pursued.
So what now?
We have learned a lot from our experiences in Visual Basic 2005. One of the things we have done is to create a team of folks whose sole charge is to investigate performance issues, and to ensure that Visual Basic Orcas will ship without the same problems as Visual Basic 2005. I can't promise anything here, but I can say that we have been working hard to make sure that Visual Basic Orcas is the best ever Visual Basic for you in many ways.
As always, please let me know if there are any questions.