I have tried oh so many bluetooth headsets (various ones by Motorola, Sony, Plantronics, the nXZEN 5500, and the Jawbone). All have had significant usability issues. Most were completely unusable in moderate wind and most were not loud enough to properly receive calls on the streets of Manhattan. Only the nXZEN and Jawbone had DSP processing sufficient to block out most street noise, but the DSP wasn't so effective in moderate to strong wind. Plus the nXZEN had relatively lousy audio quality on the receiving end of things, so it was often difficult to understand callers.At last I have found a usable headset, the Voyager 510. The audio quality of this headset on the user end of things is absolutely phenomenal. It is several magnitudes louder than any other bluetooth headset I have tried. I have good hearing so I don't expect a headset to be super loud, but most bluetooth headsets are so low that conversation from a caller can almost be unintelligible. This Plantronics headset produces clear, loud, largely static free sound.The headset also transmits audio extremely well. I spoke to several people on the streets of Manhattan and they couldn't tell I was even on a headset. I also left several voicemails for myself and the audio quality was quite good. Moderate wind is not a problem for this headset at all. However, I don't believe that this headset employs the same type of DSP as the the nXZEN or Jawbone, so if you are on a noisy street the person you are talking to may hear the background noise. However, even with back ground noise you will be reasonably easy to understand---the headset just doesn't actually block the noise as much as one that uses DSP as much as the nXZEN or Jawbone does.There are a few small drawbacks. As others have noted, the headset is larger than many out there. But it is EXTREMELY light and VERY easy/comfortable to wear. It easily fits in my pocket. I certainly prefer a headset that works well to one that doesn't work but is smaller. One other minor drawback that not too many people have noted is that the headset does not support call waiting. I find that to be a strange omission from an otherwise excellent headset. You can still use call waiting while on the headset. But you must switch between calls by using the phone, not by using a button on the headset. The headset may not be so reliable either. My first one simply stopped working after a year and I had to purchase a second one.The bottom line is that this is the best bluetooth headset I have ever used. It really works as advertised and provides a user with an easy way to make handsfree calls. Plantronics likes to advertise its long heritage of making quality headsets and frankly I am often put off by such marketing hype--but in this case, Plantronics wisely chose to release a headset that lives up to its history/marketing. I hope its next model is even better, but thank goodness Plantronics released a product that works in a crowded field full of largely half-baked products.Update As of December 19, 2007Since I originally wrote the review above, I have also tried the Jawbone headset that many people rave about. The Jawbone is quite effective at blocking ambient noise. If you regularly use your headset in a really noisy office or restaurant or with the radio on in your car, then the Jawbone may be a better choice than this one. But the Jawbone is largely ineffective at blocking out wind noise whereas the Voyager 510 is still the champ in that regard. The Voyager 510 is still the choice for me due to its ability to largely block wind noise since I make most of my calls walking along the streets of Manhattan. Also, the Jawbone is not very comfortable at all and it is very hard to get it to fit well in my ear and on my face.I should note that I had to purchase a new Voyager 510 after about a year since the first one just stopped working for no apparent reason. The new one works just as well as the old one, but the Voyager 510 may not have the best long term reliability.Update as of May 21, 2008In my opinion, the Voyager 510 has finally been dethroned as the king of bluetooth headsets by the New Jawbone. I just pourchased the New Jawbone and I have tested it in extremely windy conditions near the water on the the streets of Manhattan. I made several test calls to friends and to voicemail. The New Jawbone seems to block wind noise approximately as well as the Voyager 510 and beats it in terms of blocking out other sound. The New Jawbone is also 1/3 the size of the Voyager 510 and much lighter. Of course the New Jawbone also costs 3 times as much as the Voyager 510. Audio quality on the user end is still slightly better with the Voyager 510, but only very slightly.Please note that I am referring to the New Jawbone (which was released less than a week ago). The old Jawbone had fit, wind noise, and audio quality issues that made it inferior, in my opinion, to the Voyager 510.