Update Tuesday is here, and today it brings Office 12.1.5 and 11.5.3. Office 12.1.5 is a combo update. You must have Office 12.1.0 or later installed; if you've skipped something between 12.1.1 and 12.1.4, this one will get you completely up-to-date. For Office 11.5.3, you must have 11.5.2 installed.
For Office 12.1.5, there are security, stability, and performance improvements across the suite. Entourage gets a time zone update, and Word has some formatting improvements when saving to .doc. Excel has a bunch of fixes, including several calculation issues. For full details of what's included in here, read over the knowledge base article for 12.1.5.
For Office 11.5.3, there's stability performance improvements across the suite, and Entourage 2004 gets the same time zone update as Entourage 2008. Full details are, as always, in the knowledge base article.