From their site:" 'Zeitgeist' means "the spirit of the times", and Google reveals this spirit through the aggregation of millions of search queries we receive every day. We have several tools that give insight into global, regional, past and present search trends. These tools are available for you to play with, explore, and learn from. Use them for everything from business research to trivia answers."
It is very tricky picking the right combination of words for a fair comparison, so dont draw too many conclusions, aside from the fact that our society is quite shallow (Top searches in 2006 Google News were 'Paris Hilton' followed by 'Orlando bloom' and just then.. 'Cancer')
Go and explore.. it is very interesting.