I disconnected mine when I wasn't sure it was running right. The car didn't feel any slower. Hmmm.
After reconnecting it, the car took a mile or so to get better, then it seemed to be good for a bit before dropping off again.
Funnily enough, there was a MAF error code when I went to the dealer complaing of bad performance /ubbthreads/images/graemlins/smile.gif