Developers, do NOT get EasyTether! EasyTether allows your 3G connection to be shared to your computer via the USB Cable.

HOWEVER, when you install the computer-side client of EasyTether, it saves a file that tells the computer to automatically mount the phone as a network spot when it is plugged in. This means adb won't find it (since it's not mounted as a device), and this means DDMS and "Eclipse Run on Device" won't work either. EasyTether is a great app, but developers shouldn't get it if you test apps on your device.

P.S. I learned this the hard way. It involved deleting system files and logging in as root on my Mac, as well as a few terminal commands.