One day, some new security flaw will appear, a cloud storage service will be hacked, and people's lives will be messed up. After all, simple logic, like not putting sensitive material on the web doesn't occur to people (Facebook has proven this many times).
And, these same people will blame Microsoft, Apple, or whoever runs the service for there own inability to store there files themselves.
And, as Wombler pointed out, we can't forget the shenanigans pulled by the operators of such services.
You can assimilate my big, fat...