I agree with Pfattkat. When I draft, I definitely consider where each hitter is going to bat in the order. In doing so, you can draft PAs accordingly. I'm often surprised to see someone like Miguel Dilone batting leadoff. With his 550 PAs and .340 AVG I see him as the perfect 6th hitter in an open league. The fact that he is a decent basestealer puts him in a position to get into scoring position for your 7th/8th hitters. Plus with his AVG, he'll knock in runs hitting 6th.
So with that said, no, I would not bat a guy with 550 PAs much higher than 5th in my lineup. He would tire too quickly and as boogerlips said, you'd be stuck putting a goofy backup player in your lineup all too often. Typically, you're going to want around 700+ PA for your leadoff guy and then 680+ for your second hitter etc.
I'm talking primarily open leagues here though. I think some of this discussion depends on the league and how your team is performing. No clear cut rule, but this is a start. Another guy I like, Otis Nixon has "leadoff" type numbers with his OBP and SBs, but only about 490 PAs. Perfect #8 hitter in an open league, but if he is fresh enough and someone else needs a rest, you can lead him off as you get past the all star break on ocassion.