I use SpiderOak, it is a lot like DropBox with client side encryption. If you lose your password you lose you data.
Original promo announce: https://spideroak.com/blog/20110330182326-eric-brian-and-wor...
There is a small perceptible delay when i try to use this(rarely).
That said, their UI is comprehensive feature-wise and not as user friendly as Dropbox UX.