While I am still skeptical of how many companies will adopt responsive design test automation, I am spending time learning the Galen Framework. It's Selenium WebDriver based, so I know something of where it's coming from. I find the lack of writing code a little difficult to get used to. I like writing code, but the Galen Framework makes responsive tests pretty simple and easy to read.
A couple tips though: px ranges must read lowest to highest ex: 30 to 40px
and if you're on a company PC with tight security, phantomjsdriver will help you get up and running tests quickly. If the tests prove useful, then you can pester security for some workarounds.