Box
I'm late for the party, but I brought a prediction.
See, in few more years Dropbox will be able to afford a big ass branding agency, and a big ass agency can't design anything fancy, because it is just way too easy to pick on. So they would play it safe and suggest something simple. Something that captures the core values of the product, communicates product history and stays true to the brand spirit. Something like this shot, but perhaps they will even forgo the center square... except that these 5 rectangles would cost an arm, a leg and a small fleet of Ferraris.
So here's my prediction - this is what Dropbox logo will look like in few years. The color is probably off, but the symbol I am pretty sure is spot on :)
Do not forget to check out a supplementary brand pamflet, which explains how these rectangles are not just any rectangles and how those Ferraris are well justified, almost a bargain.