No, especially in light of fickle user tastes. Social media has a very short track record and little in the way of models that would offer guidance in growth formulas. Will these sites be like a street of bars where a movable feast ambles on from one novel watering hole to another? Or will they become more like true communities that are unlikely to change their venue unless something goes terribly wrong at some fundamental level? We'll see. At this point I'd be more on the long side of the bet than the short side, though.
