The unfortunate thing with this design is that it's quite often possible to break things by updating silently, too. My Cr-48 became almost unusably slow after the most recent update, and I seem to remember a bunch of Windows Phone 7 devices getting bricked in the same manner.

You have to have extraordinary quality control and testing on silent updates like that, and quite frankly, if OSes with a very limited number of variations on hardware can't get it right, how can we expect PC distributions to?

This is only OK when it comes from a wise and benevolent company (e.g. Google). I would not want to encourage this sort of behavior in all software (think Skype, Acrobat, etc... ugh!)

Wise and benevolent? I wouldn't encourage this behaviour from any company. It's risky and has a high chance of completely alienating your users if you don't get it exactly right, and and something breaks.

ubuntu can do automatic updates