I WISH I could remember who said it, but I applies here and in so many other areas: You must offer the consumer something MUCH better than what they already have to get them to switch from something they like. Google Maps dis this when Mapquest was the standard.
I agree with what you wrote mostly.
What dropbox could do to mess up and give Google a chance to do something much better is this: don't give people more free space when the average user struggles with the 2GB limit.
One of the things that made gmail a success was that hotmail and the rest cheaper out on space. People had to constantly clean up their 2MB mailboxes. Google might be able to do the same again if dropbox don't offer more space for free. But that would take away from their earnings, so it isn't an easy problem to solve.
