I've been using the BackBeat 903 for a about 3 months (it's a replacement for my Motorokr S9-HD) and it's been working great with my laptop PC, EVO, and iPhone 3Gs. The sound quality is pretty good and I like the "bass boost" setting. So far, I've had no issues using it while cycling (under my helmet), running, etc. and it stays in place. I also like the fact that ear piece is adjustable, since I wear prescription glasses which can be a problem for some "behind the ear" designs.
The Motorokr S9-HD which I bought before the BackBeat is definitely NOT a "one-size-fits-all" device! Although the sound quality is the best that I've heard so far in stereo bluetooth, it doesn't stay in place during any activities which require head movement. The only time that I use it now is when I'm working at my desktop PC.