I run Audyssey XT, and I'll upgrade to XT32 in my next receiver.
I do like the EQ job it does especially on the subwoofer. It is literally night/day different in the bass frequencies, so I am happy to have it. For the L/R speakers I go back and forth between using Audyssey and bypassing it. Using it, I get a cleaner soundstage, without it, it feels like there may be a few frequencies that are just a bit too loud. I run the mic *only* at the prime LP.
Huge drawback-you can't set curves for each speaker individually (without a pro kit). So for my center channel I might like to keep all the high end (Audyssey "flat") for vocal intelligibility, but on all the other speakers I prefer the high-end roll off that Audyssey incorporates (standard "Audyssey" setting). In the pro kit, you can set the level of high end roll off for each speaker.
Dynamic Volume-I'd only ever use this one "low" because med/high have way too many artifacts. They need to change how they are compressing this, why not use a multi-band compressor if they already aren't? The only time I'd turn something like this on is when watching Das Boot, for example, and the explosions were scaring the guests.
Dynamic EQ- I really like what this does for movie watching. I watch at quiet volumes, and this still allows the subwoofer to have a significant impact.
I didn't agree with how it set my crossover frequency, so I had to adjust that manually. Also, depending on your version of Audyssey, I know it downsamples hi-def music to CD quality. This doesn't bug me, but it may for those who have a lot of hi-def tracks.
The way I figure it, below 200hz the room becomes a major factor in your SQ so it makes sense to address it through acoustic treatments, placement options, and finally, filtering solutions.