Facebook's announcement a year ago that it would open up its social network to let applications from other companies on to its "platform" marked a peak for Silicon Valley's Web 2.0 euphoria.

The move touched off a wave of enthusiasm for making "widgets" - mini-applications that internet users can plant on their Facebook page or on other websites. By grabbing the attention of the millions of users on social networks, the companies making these new portable applications dreamed of tapping into a vast new market.