Dopplr is a nice little internet service tracking your travels across the world.
And, of course, is a really good example of playful interaction. The site, though simple, uses a lot of entertaining and cool features: color codes defining the places you visit, stats like your carbon footprint and so on.
Recently they provide all the users with this great infographic, summarizing everything about your year of travels. Just great.

Check out the comment by Brandon Schauer on Adaptive Path blog which sees the Dopplr idea as a long wow moment.