At Metal Toad we're big fans of responsive design, but a common snag in the responsive planning process comes when choosing what device widths to design to. Just yesterday we had a big internal debate over what the best widths to design to are for 3 layout sites, 4 layout sites, etc. I'll get to our conclusions below, but another important distinction to call out is that for each layout there are two things to consider: what the pixel width range for a specific layout should be, and what pixel width the designer should create the PSDs at.
With the latest launch of the Amazon Kindle Fire Tablet, the world is now up to more than five major Android hardware providers. Among each of these, there is also a wide variety in the screen sizes, from the smart phones to mid and larger tablets. Outside of the Android market you have the 800 pound gorilla, Apple with their iPhone, iPod & iPad. And you have RIM with the Blackberry and Nokia (who still can't decide what they are going to use).