Recently, I have had the pleasure of testing out DropBox for some off site storage.
I was not too thrilled with how they handled security, actually very lacking in my opinion.
But I guess I am not the only one who has been looking at them as well.
The article is a great read and I suggest you read it and pass this link on to others who use DropBox.
http://dereknewton.com/2011/04/dropbox-authentication-static-host-ids/
Steve