Yeah, there's actually some science behind that. Read something about how adding a personal, creative touch to info makes your brain pay more attention to it. So for some folks, the painting part isn't just fun, it's the glue that makes the appointment stick in their head. A plain list works for phoenix235 maybe, but for others it just fades into the background. The whole point is finding what actually works for your own brain, not what should work in theory. If decorating does the trick, then it's a real tool, not just play.
But does decorating a planner actually help with memory... or is it just for fun? A plain checklist might work just as well for most appointments. Calling it important feels like stretching the truth a bit.