I generally use my smartphone for reminders, simply because my phone is always with me and it's one of the tools that I use on a daily basis, virtually everywhere. I can see how putting notes on your refrigerator can be beneficial, though. But I think we'll tend to ignore them after a while, especially if there are too many notes and it gets overwhelming. Plus you don't really get "notifications" (so to speak), another plus of writing your notes on your smartphone.