Google seems to be sending out messages to a large number of webmasters who do not have a mobile friendly site, they state the number of pages they have tested and also the number of pages they deem not to be suitable. They then go on to say how these will not rank as well for be able browsing on mobile devices. We always knew this was the case but it looks like Google are now stepping up the game, it does make complete sense as I hate it when I visit a non mobile friendly site on my phone.
I think we need to watch this space as I feel a Mobile Usability Google Algorithm being launched very soon. Wonder how long Google will give us before they press the big red button!