How often are you asked by family members or friends “I have a problem with my computer. Can you take a look at it?”
A couple of times I’ve been asked to fix a CD-Rom, which has disappeared from the explorer. In the device manager it had an error code 39. Instead of letting the other fiddle with registry settings, you can tell them to install the fix “CD drive or DVD drive is missing in Windows XP or Vista”.
More fixes are available on the “Microsoft Fix it BLOG”