I know this isn't a typical hint, but the potential for embarrassment in front of large groups of people with this bug is really high, so knowing this could be very helpful ...
On the 500 MHz iBook, Keynote has what is now a known problem. It crashes the operating system reproducibly during a presentation under OS X 10.2.3. Apple's Knowledge Base covers the issue (with no real resolution) in Article 61858.
Apparently downgrading to 10.2.2 should solve the problem until the bug is fixed, but I haven't tried that yet.
[Editor's note: Normally we don't consider KBase articles as fodder for hints, but this one is clearly worth noting. I was bitten by it a couple of times myself on our G3/500 iBook (thankfully never while presenting), and it is a bad crash -- the entire OS locks up tight, which means you can't really smoothly relaunch the app and pretend nothing happened!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030129061749370