This first one is from Youtube and I could see using it to review the water cycle and the vocabulary associated with it. It is also on Teachertube.
I am on my home computer and I attempted to download drop box. I got a warning that "this file may harm your computer". I feel more comfortable waiting until I have my district laptop to start a dropbox account. I can see how this would be great to use for photos of my students, save the "movies" we made in class, and to collect videos that could be used in the classroom. It sounds very accesible and easy to use.