put a post it note on the empire state building

In anticipation of ubiquitous wireless palm devices and GPS, GeoNotes is a system with which you can annotate physical locations and read the annotations of others with your palm device.

For example, if you visit a restaurant and find the pasta to be particularly good, you can sumbit your gastronomical musing to the system. All future customers will have the benefit of your experience when they arrive. Very cool. Found via peterme.com.