Mine was done at 100K service (my MY00).

It seemed to run smoother and idle better.

 

When valves are out of adjustment, in my experience they mostly go too loose not too tight, they make a ticking/tapping noise. You get 16 valves all making a tapping noise, and the motor can sound quite bad... So fixing this definately makes the motor sound better.
But performance differences are quite rare. The tolerances are mesured in thousands of an inch, so a valve would have to be way off before it made a noticable difference. And at that point I'd image it would be making quite a racket.

 

I think its in the $200 to low $300 price range
takes about 2hours at least to do at the dealer
because of the cool down time involved

bullitt quoted bout $200, but he usually discounts me at his shop because I bought his car from him

I'm not exactly sure wat the dealers charge since mine wa free

 

It is relatively expensive at the Honda dealership. They charged me $198 on labor and $34 for a new gasket. I am SURE one of the local car shops could do it for half the price. I am assuming that I am paying at least $70 for the piece of mind of having it done by Honda (dealership service man, that is).

From my very LIMITED knowledge, I think it really only takes about 40 minutes of actual attension by the mechanic. I am guessing that I paid about 1.5 hours of labor time to have them cool the engine with a fan.........Is this how they make their [Honda] money back selling a car that costs more to make (per unit) than they sell it for.