We all have a number of ebooks, and worry about providers going out of business, ereaders failing, computer crashes. So how many backups do you have?
I am up to nine. I have three computers (laptop, netbook, desktop, in that order of use) and I have my ebooks in Calibre on each machine. I also back-up each computer. I also have my library in dropbox, so that makes 7. I also backup to an SD card, and backup just the library on a portable hard drive.
Now that I have listed all of this, it sounds kind of excessive.

How about you? How many backups do you have?