Clean Slate allows you to have a clean desktop, always. One of the great things about the desktop is that it provides quick access to your mounted volumes, DVDs and files. However, after a while, it gets bloated and filled with tons of files, and you can't make heads or tails of what you have saved there, unless you use the Finder to sort through the files. Clean Slate gets rid of this mess by putting a wallpaper over your files. Thus, when you go to the Desktop, you will only see a wallpaper, and no files. The files will still be there, though, and you can easily access them using Finder.
There are a few different ways in which this app does its magic. It can either put an image over your desktop (which means you can use any wallpaper) or it can put a solid-color image on top of your icons. You can further configure the app to only show your icons when you are in the Exposé view and to run with a hotkey, which you can use to hide and show the files on your desktop at will.
To start hiding icons you have to check the option "Hide icons on the desktop". The trial version will show you a nag screen whenever you do this, but you can close it and carry on. In short, if you need to hide all the mess that you have on your desktop, Clean Slate is a great tool for that.