I ran audyssey when I first got my axioms and was not at all impressed. It turns out that I did not follow the instructions very well (I had the mic too close to a back wall, set mic to far outside the listening area (on my side couch.) I have run without it for almost 2 years. I just re-ran it this past weekend following all guides and FAQs to a T. It turns out that I still really don't care for it. It kills the bass on my m80's and makes the vocals sound "tinny". I re-ran it a second time just to make sure and it sounded the same.
I know a lot of people have said good things about Audyssey, but I have never experienced it. I am finding that it did a great job of setting my speakers distances and channel levels, but what sounds the best is the "EQ OFF" option that audyssey has
EDIT: FYI the version of Audyssey I have used is the MultiEQ XT that comes built in the Denon 3808. I do not have the "feature pack" upgrade (Dynamic EQ and Dynamic Volume.)