I finally put up a page for Blueproxy, a handy Bluetooth RFCOMM to TCP proxy server I've been using in most of the Bluetooth hacking I've been doing for my research recently.
The current pain with Bluetooth hacking is the splintered API situation. Linux has one stack, Bluez, which it integrated into 2.4, but it's incredibly badly documented (as far as I can tell, pretty much not at all). FreeBSD has the best stack I've seen yet, based on Netgraph. MacOS X has a half-baked effort, involving setting up stuff using a GUI; however it looks like Tiger will improve this. And of course the wait continues for the Bluetooth stack in Windows XP Service Pack 2 (I refuse to risk installing it at least until it's officially released!).
The FreeBSD stack is the clear winner out of all these, with decent documentation, fewer bugs, and the most familiar interface (for example, an /etc/bluetooth/hosts file). I'm quite keen to port it to OpenBSD when I get a chance, but it does first require removing the Netgraph portions. It also looks like NetBSD has the beginnings of some code to handle the Bluetooth HCI layer; wonder how that will pan out.