The short version is: I like them. I wasn't sure when I first switched. The zero drop thing is definitely a different feel. The first few runs I felt like my calves were stressed a bit because of that. Like Altra recommends, I switched back and forth with my former shoes for a couple of weeks, and I've been only wearing Altras since that time (which was about two years ago). I've switched over to zero drop shoes for the office and everyday use as well (LEMS shoes and Tune footwear), and I don't see myself going back to a shoe with a higher heel. With zero drop, my lower back doesn't give me near as much trouble when I'm on my feet for a long time. The other nice feature of the Altra's is the wide toe box, although some other brands have caught on to that as well. I like the Ultra One's for anything up to a half -marathon distance. Longer than that, I stick with Instincts or Lone Peaks, both of which have more padding.
RE: Runner's World Half & Festival - 5k and 10k highlights