If I decide that I need tethering again and don't want to pay AT&T a boatload of money for it, I'll be jailbreaking. I already have a license for PdaNet, so it would be free to tether again.
I just bought a 3GS and am jailbreaking my 3.0 3G right now. I need to be able to tether, even if it means carrying the 3G around with me and swapping my SIM card into it. When AT&T gets their act together, or JB comes out for the 3GS then I can get rid of the 3G.
It's re-syncing all my apps 'n crap right now!! I'd always been under the impression that it was hard to jail break an iphone (guy locally does it for $50). That was EASY. Dev Team broke it down barney style.