I really like the idea. It's a nice way to go to what "probably" are the most interesting topics when you don't have much time.

I think that being able to click directly on the heatmap instead of having to close it first, and therefore not losing your visual aid, will be a big improvement.

Anyway, nice job.

P.S. I also have a problem with the height of the rows, tested both with Chrome and Firefox on W7.