Interestingly enough, some of the ultra-high-IBU beers come out the other end and don't taste nearly as bitter as mid-IBU IPAs, and they tend to have more actual flavor even. Something like, for example, Lagunitas Hop Stupid with 100 IBUs doesn't taste half as bitter as your typical 60-70 IBU IPA.

Hop Stoopid is one of the few IPAs I can stand, actually, which I find particularly bizarre because I normally don't like hops (I normally go for thick malty beers).

There is a limit past which you can't taste the difference (I mean like humans are physically incapable), I think.