Simply point Mobile Safari to http://help.benm.at, select your country, download the profile for your carrier, and install. The settings menu will add an Internet Tethering toggle in the Network section. Then just pair with your computer over Bluetooth or plug in via USB and go. No restart required. It’s really that easy.
Performance has been rock-solid in my experience, both for tethering Mac and Windows machines. Performance is terrible on EDGE and very nice on 3G, with battery life not noticeably worse than just browsing on Safari. And maybe a little bitter once the display goes to sleep. But I’m not running BitTorrent through the thing, either.
AT&T should have a killer offering on their hands once this actually ships. It would also be nice if AT&T tweaks the interface so you can turn on tethering without pulling your phone out of your pocket. Honestly, the only complaint I have. Anyone tried it outside the US? Really seems like something that should fly under the radar so long as you’re not downloading the whole Internet over it…
And, it goes without saying, this is use at your own risk and Apple will laugh at you if you brick your phone.
(And yes, I know we’re late, but I never recommend running something risky on your hardware if I haven’t done it myself. This is as close to safe as it gets.)