Originally posted by Rasker 
running AH (say a buff run) in the background while you browse will bring it to 100% easy  
 
 AH is SUPPOSED to use 100% of the CPU resources, thats why you arent supposed to have anything running in the background.
If you shut everything down thats visibly running on  your desktop, hit ctrl/alt/del and look at your CPU resources, once you quit moving the mouse around your meter should drop down to 0%, and bounce between there and 2%.  Any more than that,  you have processes running in the background eating up CPU time.  That can get you dumped out of AH or cause lockups.  
Thats all.  Carry on.