great service for getting files from one source to another destination.
I can put file(s) or pictures from my home computer and the download from other locations when needed. For work great to have those office project docs handy from remote locations.
I would however never use as an only storage or copy of files or a total backup solution, using any cloud based service.
For backup may good for a secondary solution but would have another local backup as my primary, stored off site but locally accessible. Never know when a cloud service becomes vapor when the lights get turned off.
As for security, never use to store those spreadsheets with all your office systems admin passwords, home banking info, etc, but if do use to store any sensitive info make sure well encrypted first.
My other problem is I refuse to use any service and/or app as much as possible that requires any software that is loaded on my machine to have to access with some exceptions for standard apps, and for web apps, use of the more common standard plug-ins is fine but when have that site that requires their own viewer or app, I hit the close button, Why I never run i tunes when can download mp3 files without proprietary software anytime (paid sites of course).