QuickTime in Snow Leopard is a two-part story: what you can see and what you can't. Under the hood changes show Apple attempting to make a clean break from the past, finally mothballing the grey-bearded QuickTime API from 1991. In its place, a shiny new QuickTime, capable of the demands of modern video. Except that due to legacy support, QuickTime 7 exists behind the scenes and the system calls the relevant back-end as and when it needs to.
In practice, this won't make a great deal of difference to most Mac users, but the new QuickTime Player app will. It's an odd beast, adding yet another new interface to Mac OS X - this one has a black title bar that fades when the video's playing and overlay controls not unlike those in iTunes. Things fade in and out in a slightly gratuitous manner, the controls obscure the content, and even if the player wasn't taking time to respond, it sure felt like it was half the time.
QUICKTIME PLAYER: Now offers basic recording and trimming
In terms of features, Apple giveth and Apple taketh away. QuickTime Player now has three recording options: audio, movie (from a camera) and screen, and a trimming function enables quickfire edits before sharing to iTunes, MobileMe or YouTube. There's little control over quality and export settings, and trimming is just that - there's no copy and paste, for which Apple presumably wants you to naff off to iMovie. Therefore, anyone using standalone screen recording apps won't be tempted, but for the odd quick 'record and trim' QuickTime Player's finally useful.
Sadly, some of the old player's functionality is also gone, but said player still runs under Snow Leopard. Therefore, if you regularly use things like the A/V controls, make a back-up before you upgrade, or do a custom install, where you'll find QuickTime 7 as an unchecked option.