I’ve been using this Plantroncs 855 headset for about a month. I’m generally pleased with it. The sound quality is reasonably good for music and great for voice, audio books, podcasts, etc.
The only major flaw is occasional skipping. The music drops out for about a second and then returns. I mostly notice this when walking and/or moving my right arm (which is just above the phone on my hip). It is worse with vigorous exercise and in buildings with intense RF activity (other cell phones and WiFi).
Two problems limit utility with the iPhone: 1) Apple has only implemented part of the control standard called AVRCP (play/pause works, but not next/prev track); and 2) Voice control does not activate with a simple press of the talk button (as it should). By accident I discovered that you have to press and hold the button for about 3 seconds (why?) to get the phone’s attention.
So, life in this arena is improving… but at a slower pace than one would expect. These standards are not new. I note that prev/next already works with my OSX laptop, so this feature may come with the next rev of the iPhone OS. Better voice control? — I can dream can’t I?
Update 2012: I’ve abandoned this headset because it is too fragile for everyday use. I now use a Jabra Clipper which is not perfect, but is much sturdier.