"Mobile first," is a concept that serves us well as a design tool, putting constraints on our messaging, layout, etc. But to use "mobile first" as a complete mobile strategy can lead to some dangerous lines of thought.
There's a bigger picture that needs to be seen, and it's what we've always done when developing experiences for the web. We need to put the "Experience First." Then we can think about "mobile", "desktop", "lean-back", and whatever other technologies are released in the next several years. It's not about devices, it's about users and experiences.
Presentation first given at BarCamp Nashville in October of 2011.