Via a post on Silicon Alley Insider regarding Google’s paid-click growth via analysis by Mark Mahaney of Citi quoting Comscore stats (got all that?).  Here’s the link but this is the statement regarding potential causes that got my attention:

"A macroeconomic dampening of commercial queries by searchers"

Welcome to new economic indicators.  If people are buying less, they are searching less, and they are clicking on ads less.  Internet search activity as spending indicator.