I actually really enjoy the AU rules changes, especially skills and magic, but since my 10 year long FR campaign hasn't completed yet, I wasn't going to completely change the paradigm again (already switch from 2nd ed to 3rd ed). That said, I liked some 3.5 stuff, and disliked others, so I have written a house rule PHB for my run - and I took a LOT of AU stuff that I liked: several classes, a number of the streamlined and tweaked skills (sneak and tumble come to mind), several feats, and things of that nature. When my players' characters save (or accidentally destroy) the Realms, which should take about 2 more years in the real world, if I start up a new fantasy campaign, I'll use AU as my core, and add things from core D&D to it instead most likely.
Of all the rulebooks purchased since 3.0, it is definitely my favorite non-campaign specific, fantasy d20/OGL book in the gaming library.