Interestingly, the Nexus One from Google allows users access to the engineering bootloader (allowing re-flashing with a rooted image) with a simple command sent

Interestingly, the Nexus One from Google allows users access to the engineering bootloader (allowing re-flashing with a rooted image) with a simple command sent over USB ("fastboot oem unlock"). There's even a friendly "third-party images are not officially supported" confirmation screen built in.