How can I keep "Update Notifications" from disrupting a Keynote presentation?

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?

So, is there a general way to ensure my Keynote presentation time is uninterrupted?

Unless I know I'll absolutely need network access, I just turn off all network interfaces while I'm giving presentations. This effectively blocks any auto-update routines from running without having to disable and then re-enable the feature in any piece of software I might want to use during my talk.

I'll also shut down all the programs I don't absolutely need running during a presentation. In particular email, instant message and any sort of communication apps that could cause a notification bell or a preview to pop up on my screen get shut down.

I'll pause Growl (Growl icon in menu bar -> Pause Growl) so notifications don't interrupt my presentation.

And I'll switch from any customized backgrounds I might have to some corporate logo backgrounds.

I'll even clear my browser history. Not that there'd be anything lewd, but there might be competitor's websites or company-sensitive information that can be given away by URLs that auto-complete when I start to type in the browser.

That's my usual pre-flight check before I use my laptop in public presentation.

For "big" presentations I run Keynote and give the preso from a separate demo account. I have a docked folder of shortcuts to things I might need—DropBox account, webmail access to my email, etc.—but the only login items for that account are Caffeine and Quicksilver.

If I'm giving a workflow demo I do sometimes use my main account, and generally follow Ian's suggestions for sanatizing it prior to the demo.