This Lyza Gardner article did a great job reinforcing why ems are so great: [The EMs have it: Proportional Media Queries FTW!](http://blog.cloudfour.com/the-ems-have-it-proportional-media-queries-ftw/).
You can set everything (padding, widths, etc) in ems and the site will gracefully zoom. This is nice because of the various devices that have a strange default zoom.
@GMB Re: Vertical Rhythm. Chris Coyier in [Smashing Magazine](http://coding.smashingmagazine.com/2012/10/15/css-qa-4/) had this to say:
> But I think it’s a bit of a fool’s errand to enforce perfection on it up and down every page of a website. One image inside the content will most likely throw the whole thing out of whack.
>Does it matter if the rhythm gets off? I don’t think so. Well set text will still look good. Remember: the type will still be in rhythm with the text right around it. So who cares if it’s off with text thousands of pixels away from it, and perhaps off screen? Making sure the type looks good in general is far more important than adhering to an invisible grid dogmatically.
For similar reasons as the ems w/ zoom. You don’t know how a person is viewing your website, and you want to create an experience that is flexible and will look as good as is reasonable possible in most situations.