Google Analytics is something Erik Erwitt set up for me that I knew nothing about.
Just realized it let me find out this:
All of the machines I have access to happen to be running at least 1600 width resolution - the game looks good with them. Little did I know a quarter of the visitors don't run that wide, and aren't seeing the logo / instructions / leaderboards off the bottom of the screen.
Okay, escalating the priority of screen resizing.