O_O Good question!
I'm sure the internet will become more commercialized... It will be like the whole "switching to digital tv" thing, where everything will have to be done online. XD I'm sure sites like this will still be around, but indeed a bit obscure, as new sites will pop up and push the little guys in the background, so to speak. MySpace and sites like that will be around still, but I have a feeling that they will be also be pushed aside for something new.
I suppose it also depends on the state of world... What's going on socially would prompt a change in internet "culture." The sites people view, and the things they search for will change.
Not to mention changes in technology - That would bring all sorts of new products, games, computers, etc. to the market.
I know I'd still be surfing the net... XD But who's to say... I'll be 74 by then... I might be too busy being awesome and sailing around the world to be surfing the net. LOL!