I've had a MT3G for awhile and just upgraded to a Nexus One. I still have my old phone and can use adb with the MT3G without any issues. When I try using adb with the Nexus one i receive an error insufficient permissions on the device. Here's some more info about my setup:
Clockwork Mod Recovery
USB debugging is enabled
I have the rules set up for adb
I have tried remounting and restarted adb with root permissions and have still receiving the same error. I've tried connecting to another Ubuntu box and a windows xp box with the same error.