NetSketch is an $8 drawing app with Bonjour-like sharing abilities—if you're on the same WiFi network, it will automatically detect drawings and let you jump in to collaborate PictoChat style. Coming to classrooms and lecture halls this fall. [NetSketch]
This is definitely an application that requires a market saturation point to be useful. There are similar apps for other devices that, while nifty, are rarely used because it requires all individuals involved to have the same device. If we can convince all college students to carry an iPhone, then this might be extremely useful in a classroom - though, I somehow imagine artistic interpretations of the professor rather than actual class work being the subject of choice.