How terrible would you feel if you found out a coworker waited around all night for you to send that file you promised, only to eventually realize you've already left for the day, and that file probably isn't coming?
Successful people don't always accomplish everything they planned to, or respond to every email they said they would — but they do at least let others know that they weren't able to get to the task, or make the decision, or respond to their email today, and they usually provide a status update, as well.