Apple updated iWork '09 to version 9.0.2, an update whose patch notes say, "This update improves reliability when saving some iWork documents and when playing some presentations more than once per Keynote session."
iWork is Apple's productivity suite that contains the Numbers spreadsheet app, Keynote for presentations, and Pages for document writing.
As is usual, Apple said that the update is recommended for all users of iWork '09. It can be downloaded through Software Update if you have iWork '09 installed on your Mac. It's a 45MB download, and Software Update does not say a restart is required.