This is very cutting edge stuff and occasionally it goes wrong.
As you know I moved over to Mosso a while ago and I have generally found their support to be superb and the product to be getting better and more stable.
MySQL tends to suffer a bit on all grids and clusters due to latency issues.
As a Mosso customer you must use wp-supercache to avoid as many PHP and MySQL calls as possible. It will reduce your hit count/general CPU usage too.
On a slightly different note, since you have adsense quite aggressively positioned in the individual posts template, you might want to consider installing the "No Adverts for Friends" plugin ( http://ocaoimh.ie/no-adverts-for-friends/ ). It allows you to serve ads to random visitors, but regular readers will not be served ads that the have seen dozens of times but never clicked.