Server load Tripwires.
 

It'd be pretty cool to have a plugin where you can individually configure what features/parts of your forum get disabled when a certain server load is reached:

Ability to disable standard vbulletin features on a feature by feature basis with manual inputs of required server load reached before feature is disabled.

Ability to disable individual plugins based on server loads.

Ability to deny access to certain usergroups when system reaches a certain load.