Yesterday afternoon, Apple rolled out a point upgrade to OS X Lion and we recommended you back up before installing, just in case. Turns out the paranoid voice in our head was on to something — users on Apple's support forums (as well as commenters in our original post) are reporting severe problems after updating to 10.7.3. For those unfortunate souls having issues, every single app crashes upon opening with a bizarre CUI error. This problem typically manifests itself for those who updated using the Software Update tool; users who manually downloaded Apple's Combo Update are having better luck. If your computer is affected and you're able to download and install the Combo Update on your affected Mac, there's a chance of getting the machine running normally again.
Otherwise, you're probably stuck restoring your Mac to 10.7.2 (if you have backups available) or doing a full reinstall of Lion, While some brave users have reported successfully installing 10.7.3 with the Combo Update after restoring their broken Macs, we'd advise you to just avoid this update until Apple sorts things out — with the lack of user-facing features, there's no need to rush into it.