I like to keep an eye on trending browsers/OSs/languages etc... I find google trends is a very useful resource sometimes but other times I can not get the information I want.
Example of very clear increase of Ubuntu (with 6 monthly peaks near release dates) compared with other major linux distros ecline over the years...
http://www.google.com/trends?q=ubuntu%2C+debian%2C+redhat%2C+mandrake&ctab=0&geo=all&date=all&sort=0
Example of results that are skewed because of non-programming related events. See "flash floods" and "earthquake in Java" in the news results
http://www.google.com/trends?q=flash%2C+java%2C+javascript&ctab=0&geo=all&date=all&sort=0
Is there a way to filter the results better to only include Java the programming language, and make sure that it catches all variations of a name - for example js instead of javascript, or an alternative tool that can produce similar graphical trend data.
It is possible to exclude terms with a minus sign and use | for variants:
flash -flood, java -crash -quake, javascript +js
But if you want accuracy it would be better to use the Language Popularity Index (or Tiobe as Bas suggests).