I do a lot of responsive web design, in fact it’s all I do. I want the mobile screen to always be at 100% without zooming. Here’s how I do it:
meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0"
It ensures my responsive websites look exactly as I expect on mobile devices; within reason.