I can confirm that it works, however, you do need to keep the app front-and-center to keep the connection alive. Also, it only works over USB, not WiFi or BT,

I can confirm that it works, however, you do need to keep the app front-and-center to keep the connection alive. Also, it only works over USB, not WiFi or BT, and you need to have the custom Tether app installed on your PC. Looks like it's creating an Ethernet-over-USB interface to the phone, then I can't tell if the app is contacting network servers directly, or if it's proxying it all back to Tether.com's servers (traceroute didn't want to run for me). Interestingly, if I have WiFi active on the iPhone, it routes the connection over the WiFi network, which could be really nice in certain circumstances (you pay for a WiFi roaming plan on your phone, but don't have access to it on your PC). Speedtest was showing 2.3 Mbps down, 0.9 up over 3G. Not too shabby. I only plan to use this occasionally, to check emails from the road; I hope AT&T doesn't try to yank my unlimited data plan... [I'm posting this comment over the Tether link now]