Niall Cook, of Hill and Knowlton, writes about using free online tools to study, among other things, the conversation gap. The end of his post has a form which asks for some simple data and creates trend graphs using BlogPulse' trending system. Pretty cool. I'll note, however, that the quality of results will vary greatly with respect to the ambiguity, etc., of terms. Looking for 'apple' will likely pick up mentions of the company, but also mentions of fruit.