QuickTime 7.6.6 for Leopard is recommended for all QuickTime 7 users and according to Apple brings about "general reliability improvements for iMovie." Additionally, the update addresses a long list of security vulnerabilities related to maliciously crafted audio or movie files that could allow attackers to cause crashes or run arbitrary code. The update is available via Software Update or the Apple Support Downloads page. (Free, 68.63 MB)
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Multi-Monitor iChat in Snow Leopard
In Snow Leopard, on a multiple-monitor system where you're using screen sharing over iChat, dragging the tiny inset preview of your own screen to another monitor shifts the remote screen to that monitor.