You have to know what hands he will re-raise with as well. Say the flop is A-8-3 rainbow and you hold KK or QQ, is he/she the type of player to raise with a PP of nines and up?

I would say if you don't know your opponents play it a lot more tightly until you do know them. Once you know them, then you may be able to play it further/more aggressive if they are loose players.