QuickTime users, casual or otherwise, may want to go and download the latest update. Version 7.1.5 of the player has been released, to address a series of flaws that could result in system compromise at the worst. Due to improper handling of various music and picture files, the software could be compromised from malicious files and then the system could be forced to run arbitrary code. It wasn't just a security update, however, and other functionality has been added. Amongst other security notices you can find the QuickTime flaws.
This is yet another series of patches for QuickTime that have been necessary, with the suite being compromised several times over the past few months. You can the latest update automatically through system updates on Mac OS X or you can download it yourself from Apple's site.