Confirmed on 3G
iPhone 3G 8GB:
So I upgraded to 3.1 after I mysteriously lost my signal for 2 hours (and rebooting, reseating the SIM, resetting network settings did not resolve) while my wife's iPhone was getting 5 bars of 3G right next to me.
My signal was not restored by the upgrade... but did magically reappear 25 minutes later.
Immediately after the upgrade, I wondered whether it would break tethering, so I went to view the menu item in Settings - General - Network. It was there... for a fraction of a second. I watched it disappear.
I have tried the following in an attempt to restore:
Removing the profile. Rebooting. Reinstalling the profile. Rebooting. Resetting network settings. Rebooting.
Nada.
Noteworthy: help.benm.at has a message up stating that they are working on tethering for 3.1, which seems to indicate that they have confirmed the problem.
If I had only waited or not needed my phone, I'd still have tethering. And I'm about to go on vacation.
AT&T and Apple have totally killed Kenny.