Yep, USB tethering died in Betas 2 and 3, but with iTunes 8.2 Pre-release and Beta 4, all is working again and it feels wonderfully fast. Well, it’s only running at 336.58 Kbps, but it feels great! As a note, i think the fix was actually iTunes rather than iPhone Beta 4.
Lovely 
Now to test the Bluetooth speeds
