Last year, YouTube enabled annotations, which lets users make little notes about their videos. Now, they're offering users the opportunity to open annotations up to their viewers for collaborative annotations.
To do so, go to the annotations editor under "My Videos" or on the page of your video that you want to allow the collaboration for. There will be a link that you can send out to people you wish to collaborate with.
If you don't like an annotation, you can delete it.
What do you think of collaborative annotations? Are you going to give it a try? Let us know in the comments.