Last week Google announced their plans to push websites into offering great mobile web experiences. With this announcement came some controversy over Google's preferred method of mobilisation. According to the Responsive Web Design (RWD) community, not an actual endorsement for the design technique itself.
A single URL does make it easier for Google's link algorithms to work, however no penalty will be given for not using this method. Shared HTML within RWD also means that the processing required by Google's crawler is minimised, increasing its efficiency. This means less of a technical overhead for Google, so selfishly would prefer this method. Google themselves don't employ RWD in their mobile website, but instead favour a separate, highly optimised mobile experience.
In reality Google recommend the configuration which is best for your users, which is why Apple, Facebook, Twitter and LinkedIn have chose not to adopt RWD in their mobile websites. The topic of which approach is best is still heavily debated in the web development community; however we are starting to see a large emphasis on mobile performance instead of just aesthetic design.
In short; relevant content, a great user experience and fast loading times are now becoming primary concerns, rather than just how good a website looks on a mobile device .