Congrats guys! I'm really pleased with Dropbox's success. It gives me encouragement to stay focused on solving unsexy but fundamental problems.
I actually think Dropbox has a very sexy business model. It's the Silicon Valley darling with the least amount of flaws in the business model, imo. Too many others need to police their users to take their cut, e.g. AirBnb.
I could see Dropbox becoming a large file sharing network with great access controls. The amount of data that's produced every day needs a place to be stored and accessed, even if only a fraction of it is worth sharing. It's definitely a problem that many organizations and groups have, and there are few good solutions out there.