I can crank out about 5 very good ones but after that, the form goes downhill quickly. After 10, it makes no sense to continue (ie. on my toes).
But, in my recent Chest & Back workout (from the P90X series), I did 158 of the "girlie" ones on my knees (within one hour). But, I would not advertise it anywhere because they really sucked.
Anyway, since we are speaking about push ups, here is how NOT to do them:
http://www.youtube.com/watch?v=liz575Ot1Wc
It's Kelly Ripa's push up challenge. She does an respectable number of them but the quality is not good (although I admit I admire her for the number nevertheless).