>But will Dropbox’s strategy be strong enough to fend off popular sites like Instagram and Twitter, which also store digital content submitted by large user communities? Or put more bluntly “five years from now, will I even need Dropbox?” asks Schonfeld.

I'm not sure it's fair to compare Dropbox to something like Twitter or Instagram. I think they only store photos, while Dropbox can store whatever files you need it to. I'd say the majority of people would probably store photos and videos, but there are some who like to back up important documents, books, and other work.