Mail notifications on your iPhone. Just set up a mail forward for certain emails, and they’ll be translated into a push notification.
I get really annoyed when I find myself having to do things over and over that a computer could easily do. I am also really bad at remembering to do small things that don’t seem that important.
The latest intersection of these 2 things is that I’ve been forgetting (or not bothering) to set my status as “Away” or “Back” on all the communications apps I have running when I leave the computer. This is something that a computer should be able to do itself, and something that I’m horribly bad at remembering to do.