Silverlight 4 targeted solution. Switching between loaded file tabs takes considerable amount of time. After loading (opening) a code file or XAML markup it takes 10 seconds to be able to start working. Typing in a code behind file introduces IDE thinking for 1-3 seconds and when moving a cursor between methods. Installed already suggested update to Windows XP for potential performance improvement and did not notice any better. My solution is relatively small project.
Also, I disabled showing Designer by default for XAML. I noticed when opening XAML file the VS is still processing designer surface and then quickly collapses corresponding pane to show only XAML. That's why opening XAML file in default text mode is still slow. Designer processing portion should be entirely skipped when not desired and not invoked by user.
Hint: I do have Resharper 5.0 installed and active.