Peter Merholz serves up a welcomed reality check amid all the hoopla of 'mobile first':
My concern with "mobile first" is that we'll mistake that for "mobile only" (the way that the Web was seen as the end-all be-all for quite a while) and not appreciate just what our customers are actually doing, nor prepare ourselves for what's next.
I'll be the first to admit, proudly in fact, that 'responsive web design' was clearly the right way to go. We had multiple devices and we needed some coherent way of accommodating them.
But I've never been able to comprehend why this required (at least among some) a second -- and to my mind completely unrelated -- step, namely that of having to start your design at the level of the least capable device (i.e. mobile) especially since 'least capable' doesn't necessarily mean 'least complicated'. You might as well have told people back in the old days, 'design for telnet' -- 'telnet first'!