This is great! Really nice functionality :) Aesthetics-wise, I think because it's front-and-center, it would be nice if we could make the row of buttons a little nicer looking.

I suggest:

• Starting a new row every 5 buttons or so
• Giving the option to show/hide the buttons (like this "collapse" example, but maybe from clicking a link instead of a button?)
• Possibly making the "All" button different (link instead of button? Hollow button? Disable it when everything is selected already?)