Google has put out a new Wembaster Help video. In this one, Matt Cutts discusses responsive design and its impact (or lack thereof) on SEO. He takes on the question:
Does a site leveraging responsive design "lose" any SEO benefit compared to a more traditional m. site?
Cutts says, "Whenever you have a site that can work well for regular browsers on the desktop as well as mobile phones, there's a couple completely valid ways to do it. One is called responsive design, and responsive design just means that the page works totally fine whether you access that URL with a desktop browser or whether you access that URL with a mobile browser. Things will rescale, you know, the page size will be taken into account, and everything works fine. Another way to do it is, depending on the user agent that's coming, you could do a redirect so that a mobile phone - a mobile smartphone, for example - might get redirected to a mobile dot version of your page, and that's totally fine as well."
He notes that Google has guidelines and best practices here.
This includes things like having a rel="canonical" from the mobile version to the desktop version, and stuff like that.
He continues, "In general, I wouldn't worry about a site that uses responsive design losing SEO benefit(s) because by definition, you've got the same URL, so in theory, if you do a mobile version of your site, if you don't handle that well and you don't do the rel='canonical' and all those sorts of things, you might, in theory, divide the PageRank between those two pages, but if you've got responsive design, everything is handled from one URL, and so the PageRank doesn't get divided. Everything works fine, so you don't need to worry about the SEO drawbacks at all."
And that's about the size of it.