Re: Business use?
Businesses are doing it already in much larger numbers than people think. SalesForce is the prime example. If used as a sales tool and not just CRM/support, not only do they hold your internal price lists but also full records of all current, past and prospective customers and your relationships with them.
Then you've got a whole slew of SMEs using Google Apps, etc.
Do I agree with the outsourcing of business critical data like this? Not particularly, but then again I appear to be in the minority. Co-workers have no issues uploading sensitive data to Dropbox, Basecamp, Google Apps, SalesForce, etc. I used to point out to people the risks they were taking (especially since we have internal resources for doing file sharing, collaboration, etc), but I've long since given up.