Up until a month ago, my girlfriend has used MobileMe to backup all the files on her MacBook. This turned out terribly when a quirk of MobileMe caused it to erase all of her files on MobileMe, and then sync the newly-erased MobileMe down to her computer, erasing everything. A week's worth of college essays and CS homework were gone.

Now, I am terrified of any commercial cloud-backup solutions because of the possibility of this happening. Going off the list provided in these answers, could you please help me find a good backup service that is completely one-way? I want a service where there is literally not a single line of code that has the possibility of writing to my computer's drive. I want a pure one-way backup service.