The iPhone has around a hundred entries in the dice category, but only a few sporting real physics simulation. Our just released Pip uses Bullet version 2.72.
Bullet provided us with really good response times, multiple method hooks and configuration options, a superb realistic animation, and a small memory footprint. I would recommend it without reserve to any other iPhone developers out there.
Our only gripe is the lack of better documentation; it took some time for us, with a good understanding of physics but none of physic engines, to figure out what was the best possible setup. These forums were full of good advice at this point, so my sincere thanks to the whole Bullet community!
Miguel A. Friginal
Mystery Coconut, LLC