better communication between user
With some sort of messaging system, or better commenting system or simply more social networking feature aka all user has a micro bloging system - like facebook status.
I am not sure that is the goal of openprocessing but I would love to see a social network being developed around processing. The processing forum is good - but it's a forum lacking this layer of interactivity that social networks offer.
Messaging is really tough to implement and maintain for a website at the small scale of OpenProcessing. But you are right that there should be some way of direct communication. So I will keep thinking.