One of the hallmarks of a bad website is rollover images not done with sprites. The result is that the first time the end-user accesses one of the secondary background images, the rollover doesn’t appear. This behavior really confuses users.
Additionally, one of the best ways that you can speed up your site is to use sprites for background images. However, what many people don’t realize is that lots of plugins use background images but don’t place them in sprites.
Here’s a sprite we built from existing images for a common social networking plugin.