It changes daily. I used to keep the number to a minimum, but lately I've just been tossing stuff I'm working on onto my desktop, to be filed "at a later time". There are about 8 permanents, (the default things starting with "My", recycle bin, word, excel, and a folder of photos), and right now there are about 5 folders with names like "Installed" and "Dumb", and a few more icons for some pics and/or homework-type-material. It's a little messy, but when it takes up more than the first column of my screen, I do some cleaning. The right side used to have links to all my drives, but I haven't replaced them after a format (from about 2 months ago now), nor did I use them that much, being hidden behind AIM most of the time.
Just one monitor. It's an 18" flat panel set at 1152 x 864. I have a 7 computer network in my house. A lot of the icons are shortcuts to folders on other drives. I just finished a server with that has five 80 gig harddrives and a 52x burner. On this computer that has all the icons I am putting an 80 gig with an 8MB cache in. Then I will be starting over with just one icon ( recycle bin). I'll use the current drive as a slave. I'll see how long it takes me to clutter the desktop again. :)