Some interesting thoughts on that by Steve Randy Waldman [1]. In this snippet, he's asking whether bubbles promote useful innovation:

  He went so far as to suggest that agency problems in
  the delegated investment process, specifically the inability 
  of career-minded fund managers to stay away from bubbles 
  regardless of any personal reservations, make an important 
  contribution to innovation. Steven Fazzari (whose work on 
  inequality this blog has featured before) described research 
  showing that R&D expenditures of young firms are constrained 
  by external finance and increase in bubblicious periods. 
  Ramana Nanda investigated whether investments made at the 
  top of bubbles were poor, and found that they were not. They 
  were just riskier. Firms funded by venture capitalists in 
  heat were unusually likely to crash and burn, sure, but they 
  were also unusually likely to succeed spectacularly.

1. http://www.interfluidity.com/v2/5066.html