After uninstalling and installing some applications the other day, I noticed that some of my desktop icons had gotten "broken" in that they still worked fine, but the icon was the generic icon that Windows 7 uses when it doesn't know what the file is, rather than what it was supposed to be. Changing the icon to a different one worked fine, but changing it back left the icon still broken. Let me be clear: the icon displayed, but the image was wrong, and this was only some of my icons, not all of them.
After a bit of digging, I found this link which tells you how to fix fix the problem. I'm not really sure what went wrong, but this definitely fixes the error and gets your icons looking right again.