by Jason Caldwell » December 30th, 2011, 7:47 pm
My guess is the underlying database. Slow database connections can cause lag like this. On some Cloud Computing models, such as Rackspace Cloud Sites, the Apache processes are on the Cloud, but not the database. The database is a shared resource, and also resides on a different node. MediaTemple works around this issue by providing what's called a "Grid Container", giving you dedicated database resources. If you continue to have trouble with Rackspace, I would consider moving to MediaTemple (gs).