Ever since I lived in Austin I've been getting sucked into the Iron Cactus' mojo! Its always a cool spot ... great locations, great atmosphere. Everyone always thinks its cool. But the food is almost always sub par--not bad, but just barely ok. I have had some decent fajitas there, but everything else was mediocre. Now, they do have some great drinks and a nice downtown patio. And I can't speak for the 3rd floor tapas bar.
Oh--lunchtime service is also quite slow in my experience.