You know, I created a playlist when I first became a member of the site but I don't think I've thought about it until I saw this thread. It seemed like a good idea, but usually I'm not going to sit and watch a group of youtube videos I've already seen and I use a site like Pandora for listening to music. Usually I keep my favorites easily accessible and watch one or two from there at a time while also browsing the newest videos.
When I need to see any video I just search and download it and play it.I never tried the playlist thing.