I really don't see where the need to overclock comes from anymore. Today's speeds are pretty darn fast and I'd assume that if you actually have a real need for more processing power, that you should be able to come up with the couple hundred bucks for another socket/proc.

Lately I've been undervolting to build silent systems. The latest AMD Brisbane processors at 2.1GHz can be undervolted to 1.05V and still pass my stress tests at speed, and stay below 40C with the 'silent' fan modes.