System 7.5.5 Update -- It's clear now that Apple has not yet released System 7.5.4, and in fact, according to sources, is fixing problems relating to the IR capabilities of some Macs. The update, when it comes out, will be renumbered to 7.5.5. The next mention of it in TidBITS will be when it's actually available. [ACE]
Mac OS X Zip Expanding Utility
Firefox (and possibly other applications) may ask you what you want to do with .zip archives that you download from the Internet. If you want to expand them with Mac OS X (rather than StuffIt Expander), you may be unsure of which application actually does the job. You're looking for Archive Utility (in Leopard and later) or BOMArchiveHelper (in Tiger). In either case, the application is stored in Hard Drive/System/Library/Core Services/. Don't move it from there, though, or you'll confuse matters.