If yesterday's update is causing you issues - weird CUI errors that crash apps - then downloading the combo update might be what's needed before you start running to your backups, according to this post on TUAW.

The combo updater is the full 10.7.3 fix, including all minor upgrades/patches released between 10.7.2 and 10.7.3. The update that you download from Software Update is a delta update - which only includes the most recent changes that your computer doesn't already have.