It depends on stakes.

At the stakes I play (50nl and 25nl), I see about 95 percent of flops with ANY pocket pair. My PT stats are positive for all my pairs, so I don't think this is a leak.

As far as weak aces go, if I am at a 50nl table or a particularly tight 25nl table, I am completely comfortable raising them in mid to late position. I never limp a weak ace though, unless its suited and has multiway value. I either raise them or fold them. They are valuable though. Remember, an ace-high is a 60/40 favorite over any other unpaired hand w/o an ace. There will be alot of times when you are heads up and you both miss and check it down. Your ace-high will take the pot and this adds up.

I think I generally break even moneywise on my play with weak aces, BUT they subtly increase my vpip so my big hands get more action to compensate for it, I think.