So, you can travel two paths: One where you believe that service X can absolutely-positively not loose your data for whatever reason. Or, another, where you understand that your data can be lost at any time and for any reason by both remote service X or even your local $100 USB drive.
If you choose the first path, you are going to get stung sooner or later. And, it is my contention that blaming the service provider for your total data loss is nothing more than not wanting to admit the truth of the matter.
If you choose the second path, which could sound really paranoid but is actually very realistic, you take steps towards creating enough redundancy that a single point of failure isn't going to burn days, months or years of data. And, while no absolutes exist in this world, it doesn't take much in this day and age to have a system that will almost guarantee that your data is safe from most loss-inducing events.
I consider problems like data loss to be serious engineering problems. The difference is that I choose to look in the mirror first and blame myself first before pointing the finger at someone else.
With that said, I think Dropbox is a pretty amazing service and I credit them for getting Google and Microsoft to wake up and make some similar services which are solid and different in some respects (Google Drive and SkyDrive).