My Take
Dropbox can be a very useful tool if you do not have another mechanism through which materials can be shared and dropped off. If the dropbox is open to a community of learners, they can deposit files within it. The space can be an issue, especially if you have large files such as pictures and such.
How I Use It
I have used it with colleagues and, to a much lesser degree, students. If space becomes an issue, it is not always easy and fast to expand it, let alone cheap.