[zaidf]

"I'd rather use 5-10 really useful apps than 40-50 marginally useful ones."

You answered your own question. What this means is that if you are serious about your start-up, you should shoot for nothing less than being in the 5-10 "really useful" list.

It is not easy by any means and pg has said before that as more and more start-ups launch, the difference between great ones and average ones would become more apparent.