Herman, you must have been hearing all the talk about Dropbox lately? I use it and it works great. As some commentators have been saying, if you want secure data then don't have data.
For cloud backup I would absolutely go with a brand name and not some fly by night operation (not commenting on Spideroak as I know nothing about them). Amazon S3 is the most reliable (they aren't going away) but it requires some technical knowhow to use.
I've not heard any talk about Dropbox but I have read a few design and technical bloggers reacting to the talk. So I'm not exactly sure what the talk is. But like many others have said, if you put your data online you simply have to accept a certain amount of risk. If you have the patience you can read the terms of service.