[Thrillington]

Absolutely not true in my experience.

A cell phone reminder for a one-off is easily missed during my morning routine.

A physical motion and/or out-loud speech associated with the event cements it much more effectively.

[tedajax]

To add to your argument because I agree with you quite a bit:

A post-it stuck on the side of one's monitor seems vastly superior to any sort of app based reminder. It helps that creating the post-it and sticking it somewhere is itself a physical action that is remembered much more than a few taps of a thumb.

[amptorn]

In the case of an I.O.U., the sensible approach is to put the note in your wallet alongside your other banknotes and other things which technically count as, or can be redeemed for, money, like coupons and cards. Ideally the I.O.U. should be written by hand by the person who owes you, so the handwriting serves as authentication.

[kpil]

If only someone could invent monitors that sticky notes actually stucks...

[sogen]

Yes, destroy the note immediately after or when doing the task.