Chatroulette is the latest cutting-edge online sensation. The set-up is this: you're paired in a real-time chat with a random stranger, and it's sort of like a social sumo match; if you bore or anger or otherwise turn off your chatmate, he/she will abandon you to move on to the next random stranger (called "nexting"), whereupon you, too, are immediately thrown in with someone else.
Needless to say, it can be awfully thin gruel, dominated by amorous drones looking to "hook up", and plenty of people you'd normally have little interest in chatting up. But that's part of the amusement. As with channel surfing through dozens of uninteresting cable stations, there's a certain ADD-like satisfaction in indulging your unbridled impatience while winnowing and ferreting. And also a certain inherent rudeness and cruelty, but at least it's vented in small, relatively painless bursts (social rejection in this setting, after such brief exposure, and with someone new always right around the corner, doesn't hurt very much).
But it would be easy to thicken the soup, so there's less winnowing required. Just offer "channels", allowing users to connect, randomly, with self-described stamp collectors, bored housewives, home cooks, motorcyclists, fans of various bands, or Presbyterian weight-lifters. Give me a jazz musician channel, where I can sail forth riffs and have them thrown back at me by other players (make new associations! find gigs!). Those who remember IRC - too early for mainstream and lacking a sexy roulette option (much less live audio/video) - will attest to the attraction of this sort of narrowcasting.
Chatroulette is a good first generation effort, but it's not quite ready for prime time. This enhancement, though, could drive this concept to become the next Facebook/Twitter.
Update: even better, allow people to create their own branded channels (customize the graphics, etc.). Perhaps scale back to make roulette merely an option within each channel (call them "salons" or "granfaloons"). Give proprietors a share of ad revenue so they have incentive to attentively manage and market their realm. This could all be built fairly easily/cheaply...and it would kill!