This might sound like a strange request, but here's what I'd like to do:
Know how often a certain keyword or tag is used, over time, on StackOverflow.
For example, for this keyword: "github"
How many times was it mentioned in Jan 2012, Feb 2012, March 2012, etc.
Similar to Google Trends: http://www.google.com/trends/?q=github
I'm looking for up-and-coming technologies and things that are trending. I assume that the number of mentions of a word would be an interesting indicator.