Responsive is Better Than Fast

Users are willing to wait a reasonable amount of time for results to load, or a process to finish, as long as they have some indication that their action is being processed. When users aren't sure if their button click or key press actually did anything, that is when they become frustrated.

Next time you're deciding between making something fast, or making something responsive, make sure to remember the user experience, and whether or not they will definitively know what the system is doing.