Watch videos before they have finished downloading
When you are downloading a video file to your computer using Safari, it is possible to start watching it before the download has finished. This is great for really long movies that take ages to download.
To do this just go to the downloads window in Safari (Command-Option-L) and find your video that's downloading. Click on the little magnifying glass icon to show the file in the Finder.
You will notice that the file has an extra extension of .download added to the end, and it doesn't open properly if you double-click on it. However, instead you can right-click on the file and choose "Show Package Contents". A new folder should open up, containing two files.
One will be called "info.plist" and the other will be the video you are downloading. Now you can just open it to watch the portion that has already downloaded. For some videos QuickTime will be unable to play them when they aren't completely downloaded. If you have problems, you can try using VLC instead.