It works like this:
Site A (which was previously on the server) generally gets around 40,000 unique visitors a day. It was "Dugg" (by a user of Digg.com) and roughly an additional 80,000 people per day came to Site A- with varying time slots (as it slid off the front page)
Site B had a similar thing happen, but has not had any new content, so there was nothing for the user to "Digg". (this site remains on the same server as TWT)
As a result TWT is stuck in the middle of a "traffic jam". So... I removed the main source of the problem, and put it on its own IP, away from everyone else...