They all have their uses, but seem to be just too shallow for tech, and life.
Face it, when you need an answer to a technical question or learn about something that isn’t in Wikipedia, chances are that Google will lead you to a blog post. Not a Facebook page (not indexed, and rarely technical). Not Twitter (how much can you explain in 140 characters?) And probably not Google+, either (although there is sometimes good discussion there).
Nope, you’re going to end up at someone’s blog post. Someone who faced the same problem, did their homework, pulled together from other sources, and solved the problem.
Go to Twitter for breaking news, Facebook for your friends, and Google+ for interesting discussions.
But the next time you solve a problem, how about you contribute to the world-wide-knowledgebase via a blog post somewhere?