Fashion or Fad? You be the judge, this website is a responsive design. Try minimising the width of your browser to see what happens as the screen adjusts. Now try that with some of your favourite websites! The trend in 2013 and beyond is clearly for responsive websites.
Do you need a responsive website design? Latest estimates are that approx 50% of web browsing is using a mobile device. If you understand your site visitor demographics, then the answer becomes clearer. For example, I recently traveled for an extended period and what I noticed was the pervasive use of tablets – everywhere! People were clearly using tablets to plan and plot their travel as they went along. If my business was in the travel industry, my answer would be yes for a “responsive design” website. Another important factor to consider is the lifespan of your website. If you wish to future proof your site for several years, then in my opinion, supporting mobile devices is a very good idea.