I've been working on something like this for a University Project I'm doing. We have to set up our own business and we're making an Internet Services company, one of the things it offers is secure online file storage. With even a measly 10TB Server charging a pitiful £1 per Gb per month with 128bit encryption you make on average a 1,200% profit margin after taking into account set up fees, running costs, maintenance fees and insurance; making £110,000 p/a net. It's easy to set up and dirt cheap to run.
After looking into the business side of things, I can see why they are so popular to set up now.