Google Webmaster Tools is now sending automated messages out alerting site owners if their sites aren't mobile friendly and warning that they will be ranked accordingly to mobile users. Given that mobile accounts for about 50% of web use now, not optimizing your sites will certainly result in a dramatic drop in search related traffic.
Best be getting with the times folks.
Fix mobile usability issues found on xxxxxxxxxxxxxx.com
To: webmaster of xxxxxxxxxxxxxx.com
Google systems have tested 63 pages from your site and found that 100% of them have critical mobile usability errors. The errors on these 63 pages severely affect how mobile users are able to experience your website. These pages will not be seen as mobile-friendly by Google Search, and will therefore be displayed and ranked appropriately for smartphone users.
Best be getting with the times folks.