When you're trying to watch video clips, speed is crucial. If your internet connection isn't fast enough, the video simply stops until your computer catches up.
If you suffer from such "buffering" problems when you're watching YouTube, check out a beta feature on the site called Feather. It replaces the standard web page with a cut-down one that includes the video, a reduced navigation option, only a handful of comments, and not much else. Except the adverts, of course. Those who use Feather have reported online that the amount of buffering and catching up required has diminished considerably.
You can try out YouTube Feather at http://www.youtube.com/feather_beta. As the screen shot below shows, once you've signed up, the system is active until you disable it. Turning off Feather is also just a single click.