Research by Hivemind suggests that 60% of the busiest sites are going to be impacted by the Google's search ranking algorithm update that launches today due to failing to have a mobile strategy.
Google has been recommending responsive web design to provide content to consumers, agnostic of their device, since 2012. However, two months ago it was announced that a site's mobile-friendliness was to be introduced as one of the factors that affect ranking signal.

The mobile-friendly tool provides information on whether Google considers a site to be mobile friendly. In addition to responsive sites, providing a dedicated mobile site or an indexed app are accepted mobile strategies.
As part of our research, we have considered the busiest two million sites according to Alexa to identify their mobile strategy. It was found that only 20% of sites are taking advantage of responsive design. 10% of these responsive sites were detecting consumer browsers in order to deliver a responsive site to mobiles only. This approach, typically considered a short-term solution, allows the desktop site to remain as-is while enjoying the benefits on smaller devices.

Overall, 16% of sites deliver different content to a mobile device, and of these, just over 10% redirect to a mobile sub-domain, e.g. m.hilton.com
A further way to provide compatibility, is to create an app index. This allows Google search results to deep link to pages within Android apps. This is only applicable to a small number of sites proportionately speaking when compared to the majority of sites.
Ecommerce is ahead of the curve
This mobile ranking signal change is going to significantly affect ecommerce store revenues that have previously not prioritised usability on smaller devices.