When you use iMovie to edit video footage, you can create and name chapter markers, then place them in the video timeline where ever you want. Later, when watching the video, you can show the chapter markers and jump straight to that section of the video. The chapter markers can be seen by iDVD, QuickTime Player, and Apple TV.
Your movie might be longer than you want for saving in iTunes, or sharing on YouTube or your MobileMe Gallery page. QuickTime makes it easy to save or share just a partial selection of a movie or audio file.
Make a new movie recording: If you have a built-in iSight camera, or have an external video camera attached to your Mac, you can record a movie using QuickTime, then share it with others as explained in Tips 2 & 3.
The ease with which you can share movies on your MobileMe Gallery page, YouTube, or iTunes will amaze you and your friends.
Other than "under the hood" changes that software developers will take advantage of in the future, some of the most dramatic (and most visible) changes in Snow Leopard appear in the new QuickTime Player, also called QuickTime X (pronounced "QuickTime ten").