I like copy.com because you get way more free space that dropbox and every time you get someone to sign up you get extra space, and the person signing up also gets extra space. I have 60BG for free at the moment but I think you start with 15GB. I also heard it's more secure than dropbox but I'm not techy enough to know if that's true or why it would be.
I think definitely useful for the youtube/vlog type videos. Also, I work a lot with people in third world countries that have very little budget for equipment but would like to make videos to update people about different projects and such for NGO work going on. I could see this working great for that because they could potentially buy one piece of gear and get nice audio and video. I like it.