Previews on the iTunes store!
Apple has a feature that lets you choose to have previews from the iTunes store fully downloaded before they start playing. According to Apple, the only use of this is if your internet connection is slower than 128kbps (the encoding of songs). It isn't really useful for me because my high-speed connection is fast enough for audio, but video is not always so great. I didn't always realize it at first, but video previews don't always play for the full thirty seconds because the buffer is not large enough. Enabling this feature solves this, because it lets the full thirty seconds load before starting to play.