Apple has released an updated version of QuickTime, bringing it to version 7.2. The new media suite has several bug fixes for both platforms it is available on, including several "critical" security issues. On top of the needed security updates, QT 7.2 also adds a feature that was formerly only available in QuickTime Pro., the ability to play content in full screen. Which officially makes QT catch up to the hundreds of other players that already supported such a function for free.
It also includes updates for the iPhone, enabling more integration. You can download it for Mac or download it for Windows if you so with from Apple's site.