First, thanks for the overview. Are there any databases of devices out there that record how open or closed the device is? i.e. Can you run your own programs? Are there binary-only drivers in the kernel? Are there proprietary userspace drivers? Has anyone ever upgraded the kernel? etc.
I used to buy devices and put Linux on them. That was fun, but frustrating, since the result wasn't always feature-complete.
Then companies started shipping Linux directly on their devices. That saved me a lot of time, so I decided to buy only devices with Linux on them from now on. But then I realised it's still not "my" device if I can't upgrade it.
So now I am changing my rule to be "must be upgradeable" (i.e. no proprietary drivers, ideally able to run kernel.org Linux.) I'm not so militant about user-space stuff. But I'm tired of companies that use Linux, but don't want the community to maintain it for them. (It's also a nice quality filter, as the recent Android debacle shows. Why settle for a quick hack when you can fit in with the existing functions just as easily?)
Also, I'd like to mention that Ubuntu also ships 2 ARM versions (dove and imx51).