The guys over at iBluetoothProject.com (makers of bluesn0w, which we saw earlier) have released their GUI tool, called sweetTooth. For now it does the same thing as the previous command line version - just looks a bit prettier. Essentially it can find Bluetooth devices in your area that are marked as discoverable, and print their address.
Obviously the next step (and why this is cool) would be to get full Bluetooth access going with the iPhone - stereo headphones, file exchange, etc. No word on when/if that could happen, although the iBluetooth folks say they're working on it. No ETA or example has been given, so we're guessing its a "yah lets try that next" kinda thing. Keep an eye on this project...