I have to have a to do list. If I don't, things get missed.
Most of my to do lists are created at 10:30 at night, when I was almost asleep and suddenly remembered something I needed to do. Suddenly wide awake, I grab my cell phone and send myself an email to use as my to do list.
I've tried carrying around a little planner but I forget to write in it as things come up, or I set it down on my desk and forget to take it with me when I leave the house. At least with sending myself an email it will be there on my cell phone to remind me, since I never forget my iphone.