When I was in the middle of teaching class, using Keynote, my presentation was disrupted when TextExpander discovered there was an update available and threw up a dialog box asking if I would like to download the update. Obviously, this was the wrong time to ask me. In the past, I've had a similar experience with Time Machine ("It has been 10 days since your computer was last backed up with Time Machine").
I certainly can keep TextExpander from intruding by turning off the automatic checks for updates. I could do the same with all other programs that have such update checks. I'm not sure I can turn off the Time Machine request, other than by making sure to back it up frequently.
However, the automatic updates are a really nice feature. I like having my apps updated and I don't want to make a chore out of going out and discovering if I have updates available. To a certain extent, the App Store update process may make the update maintenance easier, but I'm sure I'll always have apps that aren't MAS available.
So, is there a general way to ensure my Keynote presentation time is uninterrupted? Perhaps something I can run during the presentation to block update requests? Or a setting somewhere to keep Keynote from paying attention to any update requests?