Just like the Motorola Milestone, it appears the upcoming Droid X and Droid 2 will have a digitally signed bootloader that will prevent users from flashing custom ROMs.
The original Motorola Droid had an unlocked bootloader and that device became one of the most popular among the Android open source community, but it comes as no surprise that Motorola wants to lock their devices down.
Motorola explained their position in a blog post during the Milestone controversy:
"Securing the software on our handsets, thereby preventing a non-Motorola ROM image from being loaded, has been our common practice for many years. This practice is driven by a number of different business factors. When we do deviate from our normal practice, such as we did with the DROID, there is a specific business reason for doing so. We understand this can result in some confusion, and apologize for any frustration." Lori Fraleigh Motodev
I have little doubt that hackers will gain root access to the Droid X and come up with all kinds of cool tweaks, but the encrypted bootloader will be a major hurdle to overcome on the path to custom ROMs. If you like to hack your Android phone and mod it 'til it won't boot anymore, you might be better off going with HTC or even Samsung at this point.