Using em instead of px for media queries is definitely a bit of a mindmelter at first. However, if you're truly interested in building a responsive site, not just hitting a few target devices(1), I definitely recommend spending a little bit of time getting comfortable with the idea.
Mostly, it forces you to consider the context of your media queries, not just specific resolutions or device capabilities. This helps to future-proof your code for new devices and build for difficult-to-test for contexts, like users who always have a browser zoom level set higher than you expect.
This article really helped sell me on the idea and show me the way:
(1)I realize this sounds judgmental, I don't mean for it to be. There are plenty of perfectly valid reasons to "just hit a few target devices" using responsive design techniques instead of building a "truly responsive site".
Mostly, it forces you to consider the context of your media queries, not just specific resolutions or device capabilities. This helps to future-proof your code for new devices and build for difficult-to-test for contexts, like users who always have a browser zoom level set higher than you expect.
This article really helped sell me on the idea and show me the way:
http://blog.cloudfour.com/the-ems-have-it-proportional-media...
(1)I realize this sounds judgmental, I don't mean for it to be. There are plenty of perfectly valid reasons to "just hit a few target devices" using responsive design techniques instead of building a "truly responsive site".