There are five reasons why you should avoid having icons and folders (other than the drive icons) on the desktop:
1. Greatly increased risk of trashing, accidentally renaming, or otherwise damaging them. If you really want the clutter, ALIASES are perfectly okay put there -- accidentally trashing an alias has no consequences.
2. Storing lots of files/folders on the desktop slows the machine down. The desktop (unlike most other windows) is refreshed CONSTANTLY rather than just "on demand," and all contents within the folders on the desktop are as well. You're making the computer work harder than it needs to.
3. It looks unprofessional/messy/tacky. Maybe you don't care about this, but at some point you WILL be showing off your desktop to someone else and believe me THEY will notice.
4. It covers up the lovely picture you've chosen as your wallpaper. Why on earth would you want to do that??
5. Applications in particular sometimes do not perform properly (nor get updated) if put on the desktop. Again, ALIASES of applications are fine (though really that's what the Dock is for!).
You tell me: which one looks better to you? Left or right?
PS. For those who want a clean desktop but feel like they need to have all their files right in front of them: this feeling comes from you not learning to file your documents and understand the file system so you know where they are. Find a place in your Home folder to file your documents (even if they're just in one big messy "MISC" folder!) and then put that folder in your dock (it will stay in the Home folder, you're just creating an alias). Now click and hold on that folder in the dock and watch what happens! Instant organization!