I dropped Dropbox because they randomly disables ALL my links without mentioning anything about it to me. I didn't find out about it until I had 300+ people email me about not being able to access a file. Even after that - you had to manually delete the old share links in an arcane way & then recreate them. Really, really terrible UI.

I use Copy.com now - clean interface, but something about their sync takes longer than it should.