After the dotcom bubble popped so spectacularly in 2000-2001, a few glum years for the technology industry have been followed by an equally spectacular run. Applehas roared back from near extinction and this week became the most valuable company in history. Facebookamassed users and mesmerised investors for years before Wall Street staged what now seems a wildly overpriced initial public offering.

Predicting the demise of social media has turned out to be a mug’s game. Companies may have risen (Facebook) and fallen (MySpace) but the sector has grown and morphed in endlessly surprising ways. The habits of at least one generation, and significant parts of others, are now irreversibly changed when it comes to sharing, recommending and locating each other in real time. Cloud computing has compounded the speed of technological change. Even while the rest of the US has wallowed in recession, Silicon Valley and other high-tech pockets have thrived.

But bubbles can pop with a bang or deflate with a long, slow hiss. There is a growing feeling that an eight-year boom is over. It is one thing when non-tech Neanderthals guffaw at the very idea of Twitter, but quite another when those blessed by the Valley’s recent success worry that the gig is up.