Dropbox is pathetically slow, small and they're always pinging you trying to get you to buy more space. I abandoned their "service" long ago in favor of Synology's "CloudStation" server. Granted, you have to have a Synology network drive, but just the CloudStation service alone is pretty much worth the price of admission to me. It's free, speeds are limited only by your connection speed, and size is limited only by your drive size.
I have my CloudStation directory sync'ed with my work computer, my work laptop and my home computer. It's also accessible via Android app. I can work on schematic or code generation all day, go down into the lab and the laptop is already up to speed, go home and write some code there, and never have to think about what's up to date on which machine. I can grab my phone and view any of the above anywhere I have cell phone coverage. It's extremely fast, unlimited in size and it's better than VPN because I don't actually need a connection -- I can go in field with the work laptop and everything's already on the local drive, and will re-sync as soon as it has a connection. It's also safer in that it makes copies of everything on every machine -- a hard drive crash is pretty trivial to recover from.
Hasn't somebody made a shareware equivalent yet that operates from a computer rather than a network drive? If not, why not?