Just like the About This Mac dialog box, and the login dialog box, some text strings in Mac OS X, when clicked, can show wonders. And I happened to stumble upon this one accidentally.
On the Bluetooth System Preferences pane's Settings tab, click on the Bluetooth Device Name string to reveal details like the MAC address, adapter version (someone please confirm this?), and model/make.
Note that I'm using a USB Bluetooth adapter. If you are one of the lucky ones to have Bluetooth built-in to your Macs, your mileage might be better.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070510072820241