Keynote 4.0.3 update
Today, Apple posted an update to the Keynote presentation app (part of iWork '08). This update, version 4.0.3, says that it "addresses performance and stability issues when working with large documents."
You can download this update by opening Software Update (Apple menu > Software update) or by downloading the installer package from the Apple support downloads site.
Please note: Users must have Keynote 4.0.2 installed on their computer to install this update.
Thanks to everyone who sent this in!