So if you're worried about Dropbox not being as private as you were led to believe, you might want to check out SecretSync - Client-side encryption for Dropbox. Basically it creates a folder that will be encrypted on the client side before it's synced up to dropbox, and only accessible to you. Windows only, but mac and linux clients coming soon.
Note: I have no idea if this has been tested or verified by anyone, for all I know installing this program could sell your secrets to the Russians and talk to your mother dirty. Just sayin'. Thanks Bryan for the link.