Audyssey - flat or house curve?

How does Audyssey on the Onkyo/Integra/Denon work? Does it set the speakers to be flat or does it apply some sort of mystery house curve. (I know it sets delays and speaker volume...but that's not my question).

The reason I ask is that flat does not sound good....and there are all kinds of thoughts on what a good house curve might be...certainly it changes based on the size of one's room.
Well, you can go to the Audyssey website and see what they do.

Also, note that different devices (even among the brands you list) offer different curve options. Finally, with AudysseyPro (an expensive option), you can design your own curve.

Finally, there is a thread at AVS which offers in depth discussion and help.