Dan Ariely - unpredictably rationally - has created a free iPhone app that gives you a compliment (and hopefully cheers you up) every time you open it. Tap the screen and you get another one. Click on the thumbs up/down icon if you like/dislike the compliment and it'll learn which ones work better. If you're feeling particularly good, you can enter your own compliment for other strangers.
The problem with this, of course, is that there is no correlation to what one knows and thinks about oneself and the compliments one receives. Even the most delusional user will, no doubt, have the occasional fleeting suspicion that all these well meaning words weren't written or said with him/her in mind.
One way to counter that is to bake in some targetting into the compliment or the context - convincing all users that while everyone else can read it, the compliment really is meant only for them or for a narrow, unique and special group of which they are a member. It would also help if the user could be drawn in hoping to find something else - only to end up being foisted with a feel-good compliment instead.
But don't we have daily horoscope apps (and columns and books) that already do all that?
[Original pic by Caro Wallis]