This is a set of simple HTML pages with various viewport and media query settings, that help me (and hopefully you as well) to better understand the working of the viewport meta tag and its @viewport CSS-based counterpart. You can find a live version on http://andreasbovens.github.com/understanding-viewport/.
I made a presentation using these templates, which explains the working of the viewport mechanism, media queries, and more: http://slidesha.re/M6TRey
Thanks to Patrick H. Lauke for the grid image and report.js code.