It can work very well if you have an established Youtube account and upload videos that target a large audience. For small niches - not so well.
The sucess is amazing. You create as high of a quality video as possible and then you just submit it at like 200 video sites, and the traffic pours in. I've made the junkiest videos ever and got lots of traffic from them. Example: http://www.youtube.com/watch?v=6mlowdFCNiI That's the great part about being a webmaster and owning a site. You only need to put in time and effort and the results are sure to come.