Every now and then a concept comes along that is so simple and clever that you know it has a high chance of working - and you wish you thought of it yourself. "Graffitio" is an example of such a concept.
Graffitio works by allowing any user to anonymously create a "wall" where other users can write on. The wall is by default at your present location, but you can drag around a map to place it anywhere in your city. Once you create a wall, anybody can write on it — completely anonymously, as in the real world.
I was quite surprised to see a number of "walls" already created with 2,000 feet of my current location in Santa Monica. The anonymous nature of the posting means that there is zero quality control and moderation, while the anonymous nature solves the "critical mass" problem faced by Loopt and other location-based social networks.
Its hard to say where this concept is headed, but its clear that the forum on the graffitio website (http://graffit.io/) is showing lots of signs of activity. Lets keep a watch on this one.