I think it's ridiculous to assume anything one way or the other at this point. While I have total faith in the Android dev community in unlocking the potential of this baby, I don't think there's much to worry about. I don't see a reason for Amazon to lock down this device to Apple-like control. Everyone knows that the Nook Color, while an interesting e-reader, has been a banging success thanks to the fact that it's an inexpensive Android tablet that's easy to hack and modify. Amazon knows this as well.
They don't need to lock it down - the OS itself is integrated with all of Amazon's services, and those services will be front and center. They will have the best experience on the device, thus will be used the most. Besides, beneath the heart of it all is Android 2.3, and while Amazon did a fantastic job of obfuscating that truth, several press people noticed 'hints' of its Android roots.
People will find a way to side load applications, and I doubt Amazon will do much to stop them. Why bother? If they can build a loyal following of happy consumers who begin to show off this device to their friends and families, as well as showing them off in public, it will only help Amazon continue to build the Kindle brand and get more people on board with the product and its services.
Pissing off developers, who are *the* most enthusiastic fans of your product, by locking them out of their device doesn't make sense for Amazon. Besides, they're not selling this thing through any wireless carriers, so they don't have to kowtow to their rediculous demands of bootloader locking and such.