According to a post on MyDroidWorld, the Motorola Droid X includes a self-destruction mechanism to prevent unofficial ROMs being installed on the phone. The Droid X has something called an e-fuse chip, which basically bricks the phone as soon as it detects that the bootloader has been tampered with. Here’s a selected excerpt from the forum post:
If the eFuse failes 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 (firmware information, the kernel information, and the bootloader version) of the phone has been tampered with.
I doubt that even this would succeed in entirely blocking unofficial ROMs. BoyGeniusReport assures us that the same mechanism was also present in other OMAP3 handsets like the Motorola Milestone. In fact, one modder already seems very optimistic about the Droid X. Nevertheless, this can potentially turn out to be a major hurdle for modders. If you like to mod your Android phone, then you might want to wait or pick up one of the many alternatives.