20 years ago most people didn't own computers and most people had never even heard the word 'internet'. Predicting Facebook will be alive and well is a crazy prediction. I can't even imagine what computing or the internet will look like in 20 years. Will we even visit websites? Or use apps? Or have info fed directly to our Google Glass(es)?

Just for perspective, Yahoo is 17 years old. Infer from that what you will.

This is a good point and relates to what Stevenj said "As long as Mark Zuckerberg is CEO". I would add to that "and as long as he, and his collective team maintain the vision". Yahoo, over the years suffered from both of these missteps. Apple did to, and then the vision came back. We all know how that turned out.

What was/is Yahoo!?

Was it a search engine? Was it a portal?

Is it a news site? Is it a media site? Is it a portal? Is it a tech company?

I think Facebook will always be a social network that's focused on building its core product(s) with good technical people.

Yahoo was a portal back when portals were the thing to be... until they weren't anymore.

Facebook is a social network site when that's the thing to be... until it isn't anymore....

I'm not so sure. I recall it being quite common five years ago for small businesses to advertise their web presence as http://myspace.com/FooBar. At the time I was completely disheartened for the future of the web. Of course you never see that anymore, and since then I don't feel that there are many tech companies that don't have to worry about a similarly precipitous fall from grace.

It might be around in 20 years but I doubt it will ever be any more popular than it is now. It already seems pretty uncool (my grandma's on there but neither I nor any of my friends are) and it's gotten a pretty bad reputation, not many people are going to be too sad to see it replaced.

Shouldn't discourage anyone from doing a web startup though, people are always going to want those sorts of social sharing sites, just maybe not that one.