Random idea: VoIP barbershop quartet
Everyone likes to sing, but there’s so few opportunities to sing with other people. How about a web service that allows voice over IP sing-alongs? You’d see a list of “channels” where people are singing, and then you could join a channel and start singing along. There might be some latency issues – but you could probably overcome that by choosing to sing with people who were “nearby” (in network terms).