Retail devices DO have locked bootloaders.
But you can unlock them.
You see, in the bootloader of the Nexus One there is a secret command. A command that, when issued via fastboot, gives you the warning you see here, after which you can merrily unlock your bootloader and flash anything you want onto your device (including our superboot rooting image).
It's easy too! Google WANTS you to be able to do whatever you please on your Nexus One, but they also want you to be aware of the consequences.
To unlock your Nexus One's bootloader simply...
- Install the Android SDK
- Power on the device whilst holding the trackball to enter bootloader mode and connect your phone to the computer
- Download and extract fastboot from here (Windows, Linux and Mac included)
- Windows: from the sdk tools folder, copy "adb.exe", "AdbWinApi.dll" and "ddms.bat" to the fastboot folder
- Run a command prompt / terminal at the fastboot directory you just extracted
- Type 'fastboot-windows oem unlock' or './fastboot-mac oem unlock' or './fastboot-linux oem unlock' (as appropriate)
- Proceed on your merry bootloader unlocked way (note: you device will be wiped)
Enjoy! Big nod to packetlss for the heads up!