Why is it using Flash, despite seeming to be based on Google maps?
The square overlay on hovering over the map is rather impractical, since it seems to be fixed on an invisible grid that has a much lower resolution than the blobs on the heatmap. Worse yet, often the gridlines are cutting an important blob (e.g. Seattle) into half, making the data shown in the hover square rather useless. From a usability perspective, the obvious thing a user would want to do here is hover their mouse over a heatmap blob and see information specific to that blob, visually related to it (not a square that is halfway off).