I just got a Tungsten T with built-in Bluetooth and the D-Link DBT-120 Bluetooth USB adapter, and I wanted to do my Hotsync over Bluetooth rather than via the cradle. It turns out that the setup is rather non-obvious, and you can feel like you configured it right when you didn't. There isn't currently a hint on MacOSXHints about it, so here you go.
If you search on the Palm web site, you will see this Knowledge Base Entry that tells you how to do it. The key thing that you may not figure out on your own is that you need to change HotSync mode to "LANSync" using the LANSync Prefs menu item in the HotSync manager on your Palm. Once I did that (I had already figured out the other things), the HotSync started working.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030625103945410