A couple of things that I just heard about on .NET 3.5 SP1 that I was not aware of:
Cold startup of .NET applications. It sounds like MS has improved how they are reading data from the filesystem on startup. The feature is meant for windows gui apps. You *might* see some improvements in ASP.NET startup, but who knows.
I'm hearing that the bits should be out in the next few weeks. I've got this in a VPC right now, so it will be good to work with this on my main machine.