As people make advances every day in technology, we also lose stuff that we don't need to know anymore. When was the last time you rewound a videotape? If you can think of anything you don't need to know anymore, check to see if it's on this list of Obsolete Skills.
I don't agree with all of them (you still need to know how to compute sales tax if you are a business owner!), but it's a pretty good list nonetheless.