People have always wanted to do certain things online: search (google et all), shopping (amazon, ebay, et all), communication (email, aol, facebook, et all) are good examples. I've never really sensed a similar demand for syncing and backing up files. The idea that a single player has a 5 billion valuation implies the industry is significantly larger than that. That's what caught me by surprise.

The numbers I threw out there were just guesses (including the 20x P/E ratio); I was trying to understand the basis of such a valuation. There are some good explanations in this mini thread, yours included, but I still struggle to imagine there will be this much money in a such a service. It seems like competition would drive the free offerings to the point where the paid usage gets pretty low.

I guess what I'm really saying is that file sync/backup as a service doesn't feel like a 10s of billions industry. I don't have much real data to back that claim though ;)