If you use DropBox think again. They refuse to encrypt their data and have just appointed Condoleezza Rice to the board. She was part of a US government that is extremely anti personal privacy. Well dodgy person!
The alternative seems to be SpiderOak, a similar service to DropBox but in which your data is encrypted on your computer before it goes up to their cloud and decrypted when you get it back again.
It's a bit freaky when these absolute hawks leave government and move into the private sector — specially when they take positions with data firms!!