Somewhat related, if you're looking to compare tags from StackOverflow, I made this site[1] a couple years ago to quickly visualize how many questions and answers are out there for given tags.<p>I use StackOverflow tag count as well as Google Trends and GitHub star count to get a rough feel for how much people are using certain things, such as version control software[2], databases, or view engines in Express[3].<p>[1] - <a href="http://www.arepeopletalkingaboutit.com/" rel="nofollow">http://www.arepeopletalkingaboutit.com/</a>
[2] - <a href="http://www.arepeopletalkingaboutit.com/tags/cvs,svn,git,perforce,bazaar,mercurial" rel="nofollow">http://www.arepeopletalkingaboutit.com/tags/cvs,svn,git,perf...</a>
[3] - <a href="http://www.arepeopletalkingaboutit.com/tags/ejs,pug" rel="nofollow">http://www.arepeopletalkingaboutit.com/tags/ejs,pug</a>