I've had my Jawbone for some time now, more than long enough to put it through its paces.
Honestly, it's not worth the $119.99 retail price -- you can get solid Jabra and Motorola for half to three-quarters of that, with comparable overall performance, and better sound quality in your ear.
That said, while I wouldn't buy one again, I do find it to work reasonably well for most uses most of the time. In conjunction with Microsoft Voice Command, it offers decent voice activated calling, though far from perfect. It would be nice if there was an auditory indication that you or the other party picked up a ringing call however -- there have been a few times I've been caught off guard, having no idea someone had picked up, or I had picked up, because there was only silence, no feedback, from the headset.
Today, however, I suffered a bit of a setback -- the ear piece, the spindly alloy piece that inserts into the headset, and wraps around your ear, broke on me. While attempting to stick it behind my ear like I have hundreds of times previously, it snapped, leaving a piece embedded in the headset. I've removed that piece using a paperclip, so I have the option at least to switch ears and use the mirrored earpiece from the original packaging.