Now THIS one I see LOTS of possibilities. Like most surfers, I've used wikipedia in the past. Of the links given in Learning 2.0, I most appreciated the one for librarians. Like cruising a network or conference of fellow professionals. Lots to learn from each others trials, successes, and no doubt failures. I plan on going back to check out programming ideas for teens...
Other applications could be club postings/events, especially teen groups. One app I would have liked when I was a business traveler was a city restaurant wiki. For example, a wiki of the best restaurants in Atlanta. My favorite places to eat are usually hole-in-walls, and who else can tell you but the locals?
Very versatile app.