This is from an article in Macworld. You can find the rest of the article here
Reduce desktop clutter
The desktop can be a great place to drop stuff, but because of the way OSXhandles desktop icons, putting stuff there can also slow your system down. The operating system treats each desktop icon just like a full-size Finder window—the icon takes up a chunk of memory, and the system has to track its position and size at all times. Drop enough files and folders on your desktop, and you may start to notice side effects (such as spinning beach balls) when you’re trying to do something as simple as open a new Finder window. Here’s one simple way to cut down on the clutter (and system drag) without losing that handy storage place: create a folder or two on your desktop (call them Need To Look At and Things To Do, for example), and then move all the items from your desktop into the new folders.