Google Trends let you see the popularity of selected keyword over a date range and compare them to each others. It's good to learn about a market and get a rough idea around the search volume of keywords. For instance on the graphs bellow we'll see the "obama" as driven much more traffic during the last year than "mcCain" and peaked on the election day. However, in VietNam if we compare "obama" to "h1n1", it puts things in context.