I cant remember specifically for the Nexus One, but i believe its the same as the modern nexus and samsung devices(devices that provide an official way to unloc

I cant remember specifically for the Nexus One, but i believe its the same as the modern nexus and samsung devices(devices that provide an official way to unlock). When you unlock a device it wipes the entire device, so your data would not be at risk. I do not know if it wipes it when it relocks it, but no it is not a complicated task. All it requires is one command. "fastboot oem lock" to lock and "fastboot oem unlock" to unlock(wipes device).