One of the reasons for using
em measurements (especially for mediaquery widths) is based on the fact that we should allow the user to alter their font size to suit them -- either by zooming their browser in/out or using a custom stylesheet. While I don't disagree with this, it seems to me that this will be a very rare user... I'm curious if there are any reliable statistics on the # of people who alter the default browser font size (typically 16px)?
Somewhat related article: http://codeboxers.com/em-vs-px-vs-rem-in-media-queries/