A new technology in YouTube are video Annotations, Video annotations are a new way for you to add interactive commentary onto your videos!
You control what the annotations say, where they appear on the video, and when they appear and disappear. You can even link from an annotation to another YouTube Video, Channel, or Search result.
The first good commercial use I've seen with video annotations is the new campaign for Samsung called "Follow your Instinct" next to a nice site they created a viral video campaign based on those annotations where depending on the choice you make you go into another direction in the movie.
You'll find the first one below, never the less if you want to use the annotations you'll have to go to YouTube as they don't work when integrated.