Update: For those of you using CDMA phones (i.e., Verizon or Sprint customers), please see this response from Aliph regarding the use of the Jawbone with such devices. Ed, thanks for sending this.
If the past five years are any indication, whatever I say here will likely make it into the top 10 Google results for "jawbone" and so I've decided to make this dead simple for everyone who arrives at this page through the search engine in the coming months: the Jawbone is the best Bluetooth headset I've ever owned. Period.
When I originally got my hands on this headset a couple of weeks ago (the day it was first released to the public), I was all set on describing its technology (the web site was a bare-bones "splash" page until very recently) and talking a little bit about my experience with it, but I've been busy and back in Florida for the past week and so anything I was going to say has already been said by others.
In any event, for those of you less inclined to actually click through and read something about it, allow me to quote from the manual (I'm told this information is now available on the about page):
Jawbone is the world's first adaptive Bluetooth headset for mobile phones. Its revolutionary Noise Shield technology combines the latest innovations in acoustics, audio processing and product design to produce a quantum leap in headset performance. Not only does the Jawbone technology virtually eliminate all background noise from your call, but as your background changes it also seamlessly adjusts the speaker output so you can hear your caller's voice better. Jawbone's intelligent system of sensors, software, and ergonomic features allows you to use your mobile phone in any environment without shouting or straining to hear.
Now, normally I wouldn't be so willing to quote from a product's marketing copy, but the fact is, it works exactly like it says it does. Indeed, I can confidently claim that the video of the Jawbone in action, while a bit hokey, is an accurate representation of its capabilities. In fact, I'm at the point now where I don't want to talk to anyone on the phone unless they're using a Jawbone on their end; why should they get crystal-clear sound from me while I'm left to suffer? :P