vBulletin generates the "Server is too busy try again later" at an operator-configurable load. The trick is to set it at a level where as few people as possible see it, but before the servers are crawling. It's pretty much guesswork, since the message can be generated by instantaneous loads. "Try later" could be as little as a fraction of a second.
It would be interesting to know whether datastore is in Filecache or Memcache, and whether it's on a different machine if memcached.
Last edited by Bushfiva; 17th January 2008 at 07:49.
Reason: Removed gratuitous insult of a bozo