"To improve the search experience for smartphone users and address their pain points, we plan to roll out several ranking changes in the near future that address sites that are misconfigured for smartphone users."
Here is how the ranking changes they have made look like:
How To Find Out If Your Site Is Affected By This Change?
Visit Google home page using your smartphone and type in site:yoursite.com and click on any link other than the home page, if you are redirected to the home page then you have the misconfiguration issue that Google is referring to (doesn't mean necessarily you are affected by the warning yet, you need to follow the next steps to confirm that)
Visit Google home page using your smartphone then search for a keyword where an internal page of your site is ranking for, if you see the warning "May open the site's homepage" then your site is affected by the change. 
Check Google webmaster central smartphone URL errors (Faulty redirect)
I do not think web design companies or SEOs need more reasons to recommend mobile friendly websites to their clients but this is just one more reason for clients to expedite the process of redesigning their websites into smartphone friendly websites following Google's best practices. Responsive design is recommended in almost every post Google does about mobile website design.
Does Responsive Get Ranking Love?
Finally comes the biggest question, is there any preferential treatment for responsive websites in Google Mobile search now? What about the future?
According to Google the answer at least for now is NO however this is very similar to the site speed issue, as super speedy site may not give you a higher rankings in Google results but a slow site can negatively affect your rankings. A responsive design may not give you better ranking but if your site is misconfigured for mobile users your ranking on Google's mobile search could be affected with a warning in the SERP that will reduce your click through rate for sure.
No one can predict what other actions can Google take against misconfigured mobile sites or even desktop only websites in the future but everyone should know that it is time to take actions and make sure that every site site has the best users and search engines mobile experience.