Problem: You're having a general meander around YouTube looking for things to watch. Some videos are longer than others but a few minutes is a long time to watch a dud and you can't rely on ratings - everything being subjective.
Idea: When people upload videos to YouTube they could select a "key ten seconds" of their video. Here's how it works: When you're searching for videos you would have the option to watch just that key ten seconds (in addition to having the option to watch the video in its entirety). This key-ten-seconds option would be available for all videos on YouTube, wherever they are displayed - be it on the front page, in your favourites, in the "related videos" area etc.
Compilations: Compilations could be created featuring featuring just key-ten-seconds of different videos. So, if you're searching for Elvis you can see various ten-second segments of different videos and choose the ones you want to watch in entirety.