Dropbox's service has always been something that an engineer who wanted to, could implement with a server and an rsync alias. Their company is not built on the same technical challenges that companies like Apple and Google and Microsoft have. Their success comes from creating and (relentlessly) iterating on personal cloud storage solution for the average computer user.

Cloud storage has been (sort of) commoditized. By that I mean it's easily obtainable from a variety of different sources (Google, Microsoft etc). It's not immediately obvious which service is "better". However Dropbox does have strong brand awareness going for them. People in Tech frequently underestimate the value of an established brand.

My personal opinion is that Dropbox will continue to do well in revenue for small sized businesses and sole proprietors. However, it's medium/large business solutions do not have as strong of a reputation (things like access control are relatively new features, I had to check if it even existed). As long as they stay first-to-mind when people talk about personal cloud storage, they will do okay.

The difference between jumping from 1-10 billion to a 10-100 billion will be how well they execute on b2b solutions.