I use a Bluetooth headset in my car all the time now, due in large part to the law preventing me from holding it up to my head here in Washington State. My current preferred headset is the BlueAnt Q1 which works well and has a cool Google Android utility. I just received news that BlueAnt Wireless just introduced the new BlueAnt Q2 which looks to improve upon the Q1 with an improved form factor, new text-to-speech feature, Wind Armour Technology for noise resistance up to 22 mph winds, Bing 411 integration, Android app for SMS messages on the go, and more.
The BlueAnt Q2 provides up to five hours of talk time and 100 hours of standby time. I love that they now have a hardware on/off switch, which is something I like on the Jawbone ICON as well. The Q2 uses Bluetooth 2.1 with support for A2DP and the ability to connect to two phones at the same time, which is important for mobile phone geeks like me that actually do carry multiple phones on muliple carriers. BlueAnt has always been great about updating the firmware in these headsets and this functionality is provided here as well. I hope to get one soon to test and will post a review after I give it a go. You can purchase a Q2 now at AT&T stores for a MSRP of $129.