Cut, copy, and paste. They are deeply ingrained into word processor/personal computer culture. They are probably the first keyboard shortcuts anyone learns. They are efficient and useful. What would we do without them?
What if I told you that there was a fourth, unimplemented keyboard editing shortcut that could have saved countless hours throughout the lifespan of computers?
Cut, copy, paste, and...swap.
The ability to swap selected text with buffered (copied) text would save a lot of needless copying and pasting. This is particularly useful when filling out webforms and editing documents, and is far more useful than merely pasting buffered text and losing the underlying replaced text.
Linux could be the first to add this feature, which is probably my greatest contribution to computer science. Simple, useful, effective - Swap. Tell a friend.