This happens every few years. 1 or 2 QBs play out of their mind (Warner, Garcia, Young to name a few) and in hindsight would be worth a top pick. What ends up happening is they fall way back down to earth the next season and the guy who takes Culpepper 2nd overall ends up in the basement of his league.
The big fly in the ointment is McNabb. Why take Culpepper or Manning in the first when McNabb was a 3rd rounder and falling. You'd have every bit as much production and better WR/RB from the 1st two rounds (hopefully). Then there's Bulger & Carr who are playing well right now and were 7th and very late round picks respectively.
At any rate, it's easy to draft in hindsight and say "well I'd take Culpepper in the first", but then again, you probably wouldn't unless you were in the bottom half of a 12 team league. SA, Priest, Tomlinson, Edge, Barber and Lewis would all go very high followed by Owens, Moss and AJ, before anyone got around to thinking of Culpepper. Wayne, Walker and T Jones might even go ahead of Culpepper in a "lets draft in hindsight" scenario.