This is an odd freeze. When I switch from source view to design view for an HTML or ASPX file, the client area freezes, but I can still click on other tabs and menus.
What am I missing here? Really don't feel like reinstalling VS2008.
I had the same problem, and found one resolution.
In VS 2008, In a page that was using a master page, the either frequency while working in source view or switching to design view, IDE would freeze for 10-20 seconds.
In my master template, I had references to the Google hosted JQuery, Jquery UI, and one or two more scripts off site. These were placed directly in my master page's head section.
I downloaded the js and then by deleting any offsite references, my IDE would be smooth again in both design and source mode.
I also discovered I could put the scripts inside my ToolkitScriptManager (I'm using AjaxControlToolkit) and added the Mode="Release", and could place the http://www.google.com references for the scripts. The IDE is still working fine for me.