The move really did fix their problems back then. There were a period where they were really having visible scaling problems, with response times often getting

The move really did fix their problems back then. There were a period where they were really having visible scaling problems, with response times often getting painfully slow - apparently especially due to slow I/O. These problems completely disappeared after their move to Rackspace's managed hosting. Now it looks like they might be hitting a new barrier that might require architectural changes to overcome.