Piwik is great!
I just compressed piwik.js using shrinksafe and it turns the original size of 32,768 bytes (using version 0.5.1) into only 9,525 bytes and everything still works great (of course
To get info about shrinksafe (free to use) see website: shrinksafe.dojotoolkit.org
My suggestion is to compress piwik.js in the release version of Piwik so everybody will benefit of the smaller size and because it is extremely easy to do
Keep up the good work!