One of the feature requests I had submitted to Google a long time ago was to allow users to offer people their own personalized Zeitgeist. I am glad they finally did. I stumbled upon this idea when I wanted to gauge trends in Open Source usage. A friend of mind wrote a Python script that uses Yahoo API that pulls the number of times a keyword appears on the Web, News and Podcasts. But I think the number of time a search is performed for a particular keyword may be a better indicator.
Finally we have a product – Google Trends that details graphs and breaks down searches by region and languages. I am still not sure how to pull the number of times a search is performed. As one can see, Linux and Microsoft are neck and neck.