If you’re really using your computer, your desktop should almost never be visible.
I think this is an overstatement. If you’re really using your computer, your desktop should be your command center. I agree with Jeff, that stuffing your desktop with lots of icons, shortcuts, documents etc is not basically a good idea. It makes your desktop a mess, and its hard to command if you have a mess in your command center.
I try, as a rule of thumb, to not exceed the number of 10 files on my desktop. Thanks to this I always have just the most important files slash documents, I currently work on. On the one hand, it helps me quickly see what I have going on, what reports I have to write etc. On the other hand, having more files, is a good indicator, that I probably try to do too many things at a time, and that I should do something about it.
Second thing (where I agree with Jeff) is using minimalistic, non-distracting wallpaper. It’s more a matter of personal preference than general rule, but I just want my desktop to be clean, and not to draw my attention while I want to focus on other things. Some (like Jeff) go that far, that they use plain desktop instead of some graphics, I on the other hand have this really cute, peaceful tree found somewhere on deviantART, which matches very well my custom Windows theme. I’ve been using both (wallpaper and theme) for years, which is also a non-distracting factor, since I got so used to them that I barely even notice them.
I also could not live without two small utilities called Rainlendar and Rainmeter. You can see them both in enclosed screenshot (click it to see it full-size). Rainlendar is on-desktop calendar with list of forthcoming events and to do list. Rainmeter can provide you with weather information, system info (CPU/memory utilization network traffic/disk information and more, all depending on the skin you’re using.
Thanks to them I can check my schedule straight from the desktop, check the weather without running any website, open any of my drives in Total Commander in one click, straight from my desktop, see the time without bringing taskbar on and even when I’m not close enough to read those small letters in tray. It makes me much more productive.
One more utility visible in the screenshot, is Launchy application launcher. That’s not basically a part of my desktop, but thanks to it, I don’t have to search through menu start to run an application.
Getting back the the main topic – desktop is the starting point of your work, so make it work for you as good as it can. There is no one-size-fits-all-solution for this, but try to find something that fits your needs. Not only those aesthetical, but functional as well.