I've noticed a curious slowing of our sites on zorg as well, and it seems to be related to PHP. Adding a single line of php code (print() if you're curious) to an otherwise static HTML file slowed the page down noticeably. Our SMF forums' index page rendered from 0.05 seconds to 0.1 seconds on our previous shared host -- and in about 0.2 seconds on DH when we signed up here -- but nowadays the same page tends to render from 1.5 seconds to 5 seconds. Mind you this is a forum with around thirty posts total and virtually zero traffic (yes, this is intentional).
We are on zorg. I have seen load average go above 20 on this server, and the average during daytime seems to fluctuate between 8 and 15. Evenings and night, around 3. This seems to correspond with the rendering times for our forum's index page; the higher load average the longer the rendering time.
DH acknowledged that they had been moving people off of our server to less crowded servers, and offered to move us as well. We gave them the go-ahead on the 24th of February, but so far we're still on zorg and there's no sign of DH lifting a finger.