This is dangerous territory IMO. and Andrew Nacin is being too cocky by saying it is "incredibly, incredibly safe".
An autoupdate may be fine today but who knows what plugin will cause a site to break or even open up a security hole in the future?
I totaly lock down my WP sites. You can't login, change things .... unless a switch is thrown. I dread to think what's going to happen if an autoupdate tries to take place at 3am.
For that reason I'm not auto updating. I will carry on looking out for security alerts and updating when I am in a position to roll things back if the update breaks something.