There are several apps that allow you to use a screensaver as a desktop. Check out the "screensavers" section of OS X apps at Versiontracker. I use xBack. It's simple, unobsttrusive and lets you switch screensavers on the fly from the menu bar.
Before Jaguar, this feature was good more for novelty than anything else. Now it works without any hit to GUI performance, especially with a really fast videocard.