Google Sending Mobile-User Friendly Warnings to Webmasters

Twice in the last week I've gotten an email from Google Webmaster Tools telling me that client sites are not mobile friendly.  They look like this:

I really appreciate this because it will motivate my clients and me to get all our client sites mobile-friendly which I want them to be anyway.  It gives me a reason to urge reluctant clients to come onboard with the mobile responsive changes.  Also Google may start including mobile responsiveness as part of their ranking algorithm and this gives my web designers and me a chance to fix them before the ranking begins.

According to Search Engine Land, Google is sending these emails to a massive amount of webmasters and company owners.