I believe social networking is here to stay. Advertising dollars follow where the audience is. Off line advertising is losing ad dollars year over year to follow where the people are. Today, they're online. Imagine in 10 years...
Facebook in particular, the largest player in the social networking arena by far, has a huge opportunity before their eyes. Wait for them to start executing on them. I "only" see 2 big ones: advertising and search. Yeah, I know, many people are talking about it. But that's true. FB knows everything about most of their users (600mm people), so how long until they create a competing Adsense service? Not far I think. That's a $10bn a year, at least, for FB in the next 5 years or less. Search is another opportunity that's so huge I can't even think of the size of that market.