There's a great deal of debate and discussion about the right approaches to mobile site development in the "SEO community." Should people build dedicated mobile sites; should they use responsive design; what about dynamic serving? The debates revolve around three considerations: complexity, optimal user experience and impact on mobile visibility (chiefly in Google search results).
Yesterday morning Google posted on its "Webmaster Central" blog that desktop sites using faulty or "irrelevant" redirects -- sending people on smartphones to the mobile site homepage, "page not found" pages or otherwise the wrong page in mobile -- would potentially suffer ranking consequences in mobile search results.
Google expressed concern that "irrelevant redirects" are frustrating and disruptive to users -- and by implication reduce confidence in Google's mobile results. The company didn't address the precise ranking implications of not following its recommendations. However sites that don't correctly send people from PC pages to equivalent mobile pages will be demoted in the future.
This is part of a larger push by Google to create good mobile user experiences and reinforce mobile search among consumers.
Last year, in a first, Google recommended responsive web design. Most marketers accepted that as gospel accordingly. However Google did not say that responsive was mandatory or recommended in every single case. It's certainly the lowest common denominator solution for publishers (though not always easiest to implement).
Yet there are many reasons why "responsive" may not yield the best user experience overall (page load time, different mobile user intent, etc.). Regardless, Google is beginning to compel publishers to pay more attention to mobile user experiences (if they're not already) or suffer the ranking consequences.