I ran across this response to Jakob Nielsen that I absolutely loved, which then led me to Josh Clark's more thorough response. In a nutshell, Nielsen has questioned the approach of Mobile First and Responsive Design, instead advocating for a practice of (gulp) building two different sites, one for desktop and one for mobile with forced redirection for mobile users. The faulty premise is that mobile users need/want something different than desktop users. I won't get into it much here as both of these articles say what needs to be said. Give 'em a read!
Nielsen is wrong on mobile (www.netmagazine.com)
Why Jakob Nielsen Is Wrong About Mobile Websites (webmonkey.com)