Over the past couple of days, we've covered the December 14 expiration of the MPEG-2 Playback Component of QuickTime, which left users without the ability to work with MPEG-2 files.
We've received a number of reports that as of sometime Wednesday, an updated version of the component is available (albeit unannounced). If you purchased the MPEG-2 component separately, you need to log into your account on the Apple Store, click the "Software Download Purchases" link, and then download the updated version. If you obtained the component via Final Cut Pro 4 or DVD Studio Pro 2, you need to download it from this page on Apple's site. (You'll need to provide your FCP or DSP serial number.)