Interesting, because I have an i7 930 @ 4.2 on air as well as a 5850 @ 1GHz on air as well.
I don't think I'm missing much else by not going water. Heck, your system is actually technically slower than mine thanks to HT, and while yours might be a bit quieter I doubt its by much because I'm also a stickler for noise.
In Puffnstuff's case he's running multiple 480s, something I don't think I could deal with on air, but again we come back to cost as I bet he spent the better part of a grand on just watercooling parts.
Even then I'd probably rather just spend the money on something like a Silverstone Fortress Series FT02 case as I've seen that case alone do wonders even with multiple GF100 fermi cards and stock coolers.
Don't get me wrong here though, I'd love to go watercooling someday. Just that right now its not just the money that I find prohibitive, its the time investment. Even if upkeep isn't too bad, its the initial setup that I find prohibitive, heck I don't care for the time it takes to properly build a regular computer, I'd rather be using it than tinkering with it, hence my comment in my other post about hobby
Its just like the guys who build hotrods, they get just as much if not more out of the building process than they do from actually driving the cars.