It's a funny thing.
As soon as something becomes adopted by the masses and actually starts working as predicted, the bleeding edge folks declare it dead and move on to discover the next best thing.
Isn't that the way it is with everything? When things get popular, they are less expensive to make and distribute and so they take less effort to find and acquire. Remember when CROCS were just the ugliest plastic shoes you've ever seen? Who would wear them much less pay hard earned cash for them? I don't recall the year they became the "it" thing in footwear, but when you can find knockoffs in every shade and color, you know it's no longer trendy and just part of our accepted culture.
The same thing can be said about social media.
It used to be that only the cool kids were using Twitter. People who didn't understand the brilliance of short text messages loved to disparage the tool. Same thing with Facebook and LinkedIn. ("I'm just really too busy to get online, I don't know how you have the time to do it."people would chide.) However, once these tools became adopted by more people, those on the edge were already on to the latest and greatest.
Just because it's mainstream doesn't mean it's lame. Just because your mother -- even your grandmother is on Facebook doesn't mean you can't use it anymore.
It just means that the way we share information is moving into another, more mature stage. Is the phone dead? The television? The radio? I don't think social media can be declared dead because it is ubiquitous. I think it is a distinct form of communication that will continue to be integrated into all other forms of media.
I do think that some users have "jumped the shark." They've taken tools that were meant for sharing and have turned them into pure advertising stream. What used to be joyous about Twitter for example, was discovering gems of thought and being able to connect with anyone just by showing up and reading. Sadly, some people automate their content so much that the instant conversation, the discussion of ideas, is all but gone.
Smart marketers will remember that thoughtful, original content or commentary is the only way to stay relevant.