Adobe has released two new updates to the CS3 versions of InDesign and InCopy. The updates bring CS3 up to version 5.0.4. The updaters are available on the downloads section of Adobe's Web site.
According to Adobe,
"The 5.0.5 update is a CS4 compatibility update, containing fixes that address known issues with CS4 to CS3 Export to INX (Save Back) workflows. This update also provides key fixes in the areas of File Size, Hyphenation, Performance, Anchored Objects, Character Alignment, Step and Repeat, Indexing and Table of Contents, Text and Fonts, Dictionaries, Color, Scripting, Import/Export Graphics, InDesign Interchange files (INX), XML, Library files, Printing, and others."
Keep in mind that this is a "cumulative" update, which contains all the previous 5.0.x updates. So the release notes for the updater details all the items fixed not only by this updater, but all the previous updaters. Nevertheless, there are a number of bug fixes detailed in the 5.0.4 release notes that are not listed in the notes for the previous updates. So this is probably an update worth downloading and installing, even if you've previously installed the 5.0.3 update.