I just tried it by opening the BlogModule.ascx and it took about 2 minutes to open design view which is not acceptable however I don't believe there is anything I can do about it as it seems to be just one more of many things VS does very slowly. While I like VS and work in it everyday I say its kind of a resource hog and is much slower than I would like almost all the time.
To be honest design view is not useful to me at all so I never use it. When I'm doing design I'm working stricly in CSS and then just refresh the browser. When I want to add controls I just do it right in the markup view, there is good intellisense so its not difficult.
I know you were hoping for a better answer, wish I had one for you.