I use youtube and teachertube often. Here are 2 videos I found useful in my classroom. The first one(from teachertube) is a grammar game for younger students, but I adapted it for older kids.
The second video(from youtube) was used as a student example for a video project assignment. I wanted my students to use color, black/white, silent picture, still shots, slow motion, and captions for their video. This video contained all these elements.
As far as copyright and fair use, none of the information was new to me.
As far as the dropbox goes, it gives me and my students 1 place to store and access student videos/projects.