I'd certainly say it's an overall positive in my system, even if it isn't perfect.
Unlike Mark, I've only got one small seating area for two people that I care about sited right in the sweet spot, and IMO Audyssey does a fairly good job balancing out the sound of my Klipsch speakers at those positions; I noted the difference was considerably more natural than stock when I switched from an older HK receiver to my current Onkyo, and got it a lot closer in this regard to my bedroom system (which has no RC, and sounds fantastic).
My main gripe is that I get one curve with my receiver, and only one curve: the Audyssey/Movie curve. I don't mind the rolled off treble; I'd even guess it might be part of why I feel my Klipsch RF-5s sound more natural. The bass boost OTOH I could live without. Even without Audyssey, I had a naturally rising low end that was a little hot compared with the mains; with Audyssey, it's boosting that even further. I don't mind the audible results (a little extra bass doesn't bother me
), but I think it's rather stupid of it to boost in the 20Hz region
A. because that tends to be hard on subwoofers...
B. because it doesn't need to be boosted in my system...