I wrote a fairly elaborate newsletter regarding the lessons I learned from responsive design. There are no absolutes when it comes to this. The decision varies from site to site.

If you believe that all websites should be responsive, then please read my newsletter. How my revenues went from $25k to $19k / month average when we redesigned and went responsive. How changing it back has now boosted the revenues even higher than before.

http://eepurl.com/przMX