I second what Eric Mann said: Automatic core updates should be OPT-OUT for new WordPress installations, but OPT-IN for existing WordPRess installations.

I'm all for the decisions, not options philosophy, but I'm also (and even more-so) all for the philosophy that, all else equal, new features in core should be disabled by default in existing installations, no matter how major or minor the feature. First, do no harm.

And I would instantly enable the automatic core-update feature. What would be even cooler would be to have WP-CONFIG options to automatically update to RC and beta releases, or even to bleeding-edge nightlies. (Sure, I do this now, with Westi's Beta Tester Plugin; but doing it via one line in WP-CONFIG would be even better.)

And I agree with everyone regarding Plugins and Themes.