Word. I'll stick with the likes of younity for a "personal cloud" - private, secure, free and unlimited.
The solution might also be to have your own cloud instead of using a public cloud. Personal clouds seem to be growing in number over the last year. None are perfect yet, but I've used younity for a while and find that it is far and away my favorite option. The beta has expanded fast and features are added every month or two. The benefit is I have *all* my files accessible via my mobile devices, but no one else has any access to my data (it isn't stored online). And it's free to boot.
it hasn't been released yet, but goes in to beta soon. it is different than dropbox in that it is much less file sharing/collaboration oriented, but it does a lot of what some people have asked for- complete transparent sync across all device types. you can sign up at http://getyounity.com/