Interesting and quick read on IXDA on Linked In: Mobile First is a Hoax. (If you’re not a member, sign up!) The long and short of it is the writer’s opinion that Desktop First results in a better final product. He makes some good points, but ultimately, I think Mobile First focuses you better on the most important items first.
One place I do agree with the author completely – you can’t just design for mobile (or desktop) and expect a responsive framework to do all your work for you. You really need to plan out the experience for different sized devices. And in my experience that means desktop, tablet and phone, despite the fact that screen sizes and touch vs. mouse are rapidly changing and proliferating.
As always – let us know your thoughts!