Man, this is really really cool! I can even reply to and originate SMS messages with this. But, as always, there's a couple of catches:
First, I was doing this with my iBook and the Belkin USB BT adaptor, and I noticed that I was having a great deal of difficulty with websites loading very slowly or not at all. Pretty soon Mail started complaining about time-outs, etc. too.
After a bit of troubleshooting, it seems that the proximity of the BT adaptor to the iBook was a contributing factor - the closer it was, the worse the problem. It would seem that it was interfering with the 802.11 wireless on the iBook. I was doing a large download, and it was popping along at around 3KB/sec and as soon as I turned off the Address book integration, it jumped up to 60KB/sec (normal for me). If I put the adaptor on an extention cord, getting it away from the iBook, the problem was still there, but tolerable.
The Belkin adaptor has multiple power output settings that the Windows client allows you to change, but the Apple drivers don't seem to know about this, so it runs at full-power all the time, apparently.
Second, does anyone know what this does to the standby time on the phone? I assume that maintianing an active connection (the phone indicates this as well as the computer) the whole time affects this. Any idea about how much?