David Sacks of Yammer wonders if Silicon Valley - meaning the venture-backed bastion of innovation and wealth creation in the Bay Area - has started to lose it's mojo. His argument - more of a handwave really - is that a/ the economics don't work in a system with such large incumbents (like Google, Microsoft, Apple, Facebook, etc.), b/ partly because todays agile, ramen-fueld startups don't have the cash to effectively compete against the incumbents, and c/ the number of ideas that can be juiced into existence given that context are few.