I have a palm Pixi+ that sits in my glove box that I use as a hotspot when needed. I was surprised that my new iPad2 can tether over bluetooth to it with no jailbreak.
Here is what I did:
Turn on bluetooth on my Pixi
Turn on the hotspot feature of the Pixi
Paired my iPad to the Pixi and turned off cell and wifi
Browsed the internet!
I wonder how it effects the battery as I haven't had too much time to test it out but it's pretty nifty to do. I paid $55 for the Pixi off contract from buy.com and threw it on a spare line I had. Since the Pixi comes with free hotspot, it works out much better than tethering to my old Droid phone, at least its more legal.