General Approach in Zen-Theming: 3 different fixed-width layouts based on viewport-size
Zen 5 has mobile/responsive built-in, and it works really well. I found the conversion from Zen 3 fixed to Zen 5-Responsive fairly easy, and I went with the dev version (Jan 2013). As suggested, you could take out all the sidebars, but they don't really get in the way.

I had to spend some time learning responsive images, in particular responsive background images.