After recently migrating my site to a Media Temple (dv) server I noticed it took a huge hit in initial response performance. The site would take 4-5 seconds to even start loading. Static pages on the same server (and domain/site) would pull up immediately.
I tried all the normal performance-increasing tricks, and scoured the forums for any other hints. I finally tracked the problem back to improper permissions set on the EE cache folder. Setting them back to 777 solved the problem. I feel like such a cotton-headed ninny muggins — this is EE basics, people!
Just wanted to document my findings here in case anyone else ever has the same issue. REMEMBER TO CHECK FOLDER/FILE PERMISSIONS after each install, update, and migration!