We've switched to it
Definitely look at that thread. You might also want to check out mortality.net's
official forums, though the stuff in there is from people with the system already and might be "too much information" just for someone evaluating the product.
As for the question of whether it's being used or not, my group has switched over to it mid-game (after switching to 3.5E mid-game, my players are ready for us to stick with a ruleset for a few months

). I can say that the player of the wizard is much happier being able to make items with this system. He's already used the system to create a couple minor items. I'm much happier as well, with a much more concrete system in place to help me balance out magic items and whatnot.
Speaking completely frankly about the book, I think it's a great system. I think the book itself could use a little reorganization -- sometimes I feel like it needed one more editing pass. Also, there's tons of flavor stuff in there, but most of it isn't going into my game because we've been in the game long enough that adding a lot of it in would change too much.
One thing going to this system will do is force your DM to think about magic items very carefully. In the process of going to this system, we've removed all magic items which duplicate class abilities or feat abilities because we think it hurts class usefulness. Due to the nice little warning signs the author has presented in the book, we've decided not to have any magic items (other than spell completion) based off of "Personal" range spells -- otherwise, you take some of the uniqueness of the original caster class away. Etc.
While the system does add flexibility in creating items, it relies heavily on the idea that any power you might want in a magic item can be duplicated by a spell. That seems like a minor assumption but it actually has a huge impact. If you want to introduce really rules-breaking magic items (like some items are) you have to be prepared to either have it be "lost magic" or somehow rationalize what level magic spell could be used to duplicate your rules-breaking item.
Think of AH as a toolbox full of great stuff. You probably can't just pick it up and start using it, but it will give you the tools you need to overhaul your magic item system and make it more sensible.