In a post to the Official Google Blog on Feb 26th (2015), Google announced:

"Starting April 21, we will be expanding our use of mobile-friendliness as a ranking signal. This change will affect mobile searches in all languages worldwide and will have a significant impact in our search results. Consequently, users will find it easier to get relevant, high quality search results that are optimized for their devices."

"Mobile Friendly" is now amongst the SEO algorithm mix along with Structured Data ("Rich Snippets").

Here are a list of useful tools/websites to help you check your current Mobile/Structured Data performance:

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