Definitely NO automatic updates.

With some of the sites that I look after Wordpress updates have managed to break some on upgrade. Some of the simpler sites could probably cope with this. With the number of plugins and themes now available how are they possibly going to regression test core each time before it is released. Look at all the Jquery issues that have arisen with 3.6.

Definitely opt in and easy roll back to previous version is a requirement for me.