Tim Oren has a great post on SV4.0:
"The Next Big Thing is a narrative we lay on top of the events after they happen, when we make our myths of the FairChildren, Steve and Steve, and kids from Cham-bana who changed the world...All a mirage, induced by survivorship bias...
...But just keep it in mind the next time the Valley Grail Quest gets trotted out by the punditocracy. There will eventually be a Valley 4.0, but the odds of any of the folks up on stage with their sunk investments - or you - calling it in advance aren't very wonderful. Most likely, it will hit rudely from behind, when least expected."
How true is this. Let's count all the failed Big Things of the last few years: push marketing, convergence (of about 27 different kinds), tablet computing (again), portals, etc. Now we've got little bubblets in social software, P2P networks, and WiFi. I think the real disruptions are going to come from left field - and these technologies are going to be interesting, but not what people will look back on as the Big Thing.