[cesarb]

> Updates on shutdown make sense in some of my machines but are awful in the laptop I use to teach classes.

It's also a bad idea when the power has gone out and the UPS battery will last for only a few more minutes. Or when you have no UPS, a storm is coming which you know will cause the power to fail, and you want to orderly power everything off as quickly as possible (not to mention that losing power during a software update is not ideal).

Which is why I love the way recent Gnome does it: when powering off, the confirmation dialog has an unobtrusive checkbox (checked by default) which selects whether you want to run software updates before powering off. If you're not in a hurry, you can keep it checked and wait for the software updates to finish; if you're in a hurry, just uncheck it before confirming and it'll turn off immediately.