Mobile Crunch reports Motorola has put a kill switch in the Droid X to prevent you from modding your phone:
Here’s what eFuse does. This information is a couple days old but it’s worth reading if you’re interested in Android, development, or open standards in general. Besides, I just found out about it, so you have to read my words whether you like it or not. or you could just stop reading. Either way. Anyway:
If the eFuse fails to verify this information then the eFuse receives a command to “blow the fuse” or “trip the fuse”. This results in the booting process becoming corrupted and resulting in a permanent bricking of the Phone. This FailSafe is activated anytime the bootloader is tampered with or any of the above three parts of the phone has been tampered with.
It requires a hardware fix, apparently, only available through Motorola, of course. This is the equivalent of a MacBook detonating some core component if you try to install an OS to dual boot.