Basically there are three layouts now -- 4, 3 and 2 columns -- depending on how wide the window is, by using @media selectors. I tested this in Safari, Firefox, Opera and Opera Mobile on OSX, and on iPhone and iPad, but I'm not totally sure that measuring "max-width" in "em" is a portable thing to do.
I've made some changes to the CSS on the calendar to (try to) make the layout look prettier in various sizes of windows and phones. Please take a look and let me know if it screws up (or even just looks ugly) in your browser or on your device. Try out various window and font sizes.