I think we're at the limits of what can be done with air cooling.
If anything we're moving back from the limits, with the death of Prescott etc. Also, even when Prescott was around, we weren't anywhere near the "limits" of air cooling; it was nearly impossible to cool Prescotts quietly
with air cooling, but that's not the same thing as being unable
to provide enough cooling. Get a big enough fan with enough CFM (you can get 120mm fans that provide up to 220cfm!
) and it will cool just fine; you might need earmuffs to stand the noise though.
Hey, you've got to take my quote in context. We're talking about air cooling the latest hardware taking into account performance and "noise".
Sure you can get a a quiet system using air cooling on a less than cutting edge components, but that's a given. It's really hard, if near impossible, to get a core 2 extreme and 2 8800 GTX's in SLI, running almost silent while overclocked using only air cooling.
But you can do it with watercooling.
(and before we start quoting again, I admit, it is "technically possible" to achieve the above using air cooling with very good earmuffs and earlugs)