I used it here and there. It was never very good, but it was a neat trick to run Finder on a Unix.
I first used it around 1996, at work. I didn’t have to do much Unixy stuff on it; I get the impression now that it was there because of a military contract. I later used it in 1998-99 for fun in college, and was struck by how much better NetBSD was on the same machines.
Now, I have an SE/30 and a Quadra 840av. A/UX doesn’t run on the latter, and I’d prefer not to waste the former on SVR2 :)