the wired article about the SDK implies that ATT didn't have a problem w/ tethering, so the probelm may be w/ apple not them. What I don't get is why apple would care one way or the other. Or actually, you'd think they'd want the revenue....
Maybe there was some sort of technical glitch and it's only gone down temporarily... (probly wishful thinking...)
Not to mention the fact that AT&T have no problem with tethering, chat and VOIP apps for their Symbian, Java and Windows phones. It looks like Apple are bunch of control freaks.