That's cool, but you should probably grey out the area either above or below that diagonal line of places where memes intersect themselves. Otherwise, there are two boxes for each combination (books+long_tail and long_tail+books), which can get confusing.

It also might be cool to be able to click on a row or column heading and see a list of all the mashups that include that meme.

Very good, that slipped past me. I fixed it so now no matter where you enter a comment for "books + long tail"/ "long tail + books" it will fill both cells.

I've also implemented your suggestion of clicking a heading to be taken to the overview for that word (left-side heading column will work now).