Mobile sales have already overtaken desktop sales, and mobile Internet usage is predicted to overtake desktop internet usage by 2014. It is only logical that mobile search will overtake desktop search at some point in the near future as well.
Responsive web design(RWD) is a web design approach aimed at crafting sites to provide an optimal viewing experience—easy reading and navigation with a minimum of resizing, panning, and scrolling—across a wide range of devices (from mobile phones to desktop computer monitors). Read more at Wikipedia
As smartphone and tablet adoption rapidly increases, so does the importance of mobile-friendly websites. If SEO is a core component of your digital marketing strategy, having a mobile–friendly website is becoming essential.