I've used this in the past and need to do so more often. These are the kinds of notes that people keep on or in their desks; they're not just tossed aside. And even taking the time to write such a missive tends to show some thoughtfulness on the part of the sender. I've met some of the team as well, and they're all class acts.
I love this service and plan to try it out soon. Wish there were more design options to choose from.