Every site I’ve built in the last couple of years incorporates a device-responsive layout using media queries to serve different styles to different device widths. (Except for one, which used device-detection at the client’s insistence, but I don’t like to talk about that one.) I’m not unique — every developer I work with can probably say the same thing.
Making a responsive site costs a little more than a static, fixed-width site, as everyone should know by now, but given the trends in mobile-device usage and search engines’ inclusion of “mobile friendliness” in their ranking algorithms, those of us still building static sites have their heads in the sand.
Google is trying to help yank those heads up (actually, they’re trying to help themselves by improving the quality of their search results, but we can pretend) by providing a simple pass/fail tool to tell you if a site is Mobile Frieldly, here. It’s also avaialable via Webmaster Tools.