So do I, it's crashing even when the server isn't busy.
I've increased the max number of connections on MySQL and Apache and I've also decreased the KeepAlive time to 2. Things, at the moment, seem to be running swimmingly. Mind you, things have been running swimmingly about ten times today only to go to shite a bit later on.
I think that it may be that Max_Connections for Apache, as it was only 100, was creating a bottleneck. Each instance of Apache had a KeeopAlive time of 15, so when the server was getting hammered, each instance was busy for 15 seconds.
I'm waiting on the vBulletin dudes to suggest optimum MySQL and Apache settings so that we can draw a line under this.
Server load averages: 1.87, 2.08, 2.09.