i own a pair of knee wraps that i bought from APT but stopped using them. i was only using them on 465+ squats and it was hard to judge what weight i could do because they do definitely give you a nice boost up.
plus, my frame of thinking is..."If the muscle can't do the weight—the muscle shouldn't do the weight." that is how i feel about pretty much all of PL gear in general. if your body was strong enough to squat 700, than you wouldn't need wraps and a squat suit, etc. overloading your body like that is just a quick way of getting injuries. that is just my personal opinion. the last 2 times i've used my knee wraps i've gone hard and heavy and have ended up almost tearing something both times.
on another note, after seeing what Big Dave had to say about knee sleeves, i kinda want to try that route. less "boost" to your normal raw squat AND i'm all about preserving your joints and tendons so you can stay in the game longer.