I would say Opt-In to automatic updates.

I manage a number of sites running WordPress. Some already do auto updates via an option the host provides. But I like to make sure I have back-uped up other ones before I update.

I can see the benefit to Opt-Out, all the LCD users automatically get updates to a more secure version. But I worry about WordPress deciding (due to bug or other) that it should change my setting to the default automatuc upgrade.

Perhaps having an option when you first install WP asking if you want to have it set to auto update, or when you upgrade WP, would be a good idea.