I am a vim user (neovim, actually, but that is a post for another day), and since it relies entirely on keymappings to perform specific editing functions, anything I can do to help my fingers travel a little less on the keyboard means huge productivity gains over time.
While this is not a new hack, it is certainly my favorite. I don’t use the caps lock key for anything, so I have made it more useful by remapping two other keys to it: when I tap caps lock, it functions as the escape key, and when I hold it, it acts as control.