I don't have covers for most of my devices because they are incredibly expensive. I also doubt that these covers provide much beyond cosmetic protection, which means that they aren't even worth the price.

The two exceptions: my Kobo Touch has a cover, since it was given to me. I bought a padded sleeve for my MacBook, which was $2.50 at a dollar store. (That's about 5% to 10% the cost of sleeves that computer stores carry. The hilarious part is that the dollar store version provides more protection than some of those computer store sleeves.)