How to check if your site is mobile friendly:

Is your site mobile-friendly? If you answered “yes” then excellent. Just relax and wait for it to start climbing higher in Google's search rankings starting Tomorrow: April 21. Because that's the day Google has promised to modify their search ranking rules to give preference to mobile-friendly sites.

If not, you have a ton of work to do. If you're going to attempt to do this on your own, you should start by using Google's mobile-friendly test page to find out whether some of the pages on your site work well on smartphones, tablets, etc. If you want to analyze your entire domain, you'll need to use Google's Webmaster Tools. Doing so will provide you you with a comprehensive report. (Naturally you'll need to have Google's WMT integrated into your site to take advantage of this.) Hopefully you can avoid a massive redesign but from my research so far, get ready to spend  several dozen hours fixing everything that fails these tests.

Google's Recent Statement on Mobile Search:

“When it comes to search on mobile devices, users should get the most relevant and timely results, no matter if the information lives on mobile-friendly Web pages or apps. As more people use mobile devices to access the Internet, our algorithms have to adapt to these usage patterns. In the past, we've made updates to ensure a site is configured properly and viewable on modern devices. We've made it easier for users to find mobile-friendly web pages and we've introduced App Indexing to surface useful content from apps.”.

According to Google, its choice to examine “mobile-friendliness” for use in computing search rankings will affect all mobile searches on your site. It will also have a “significant impact” on Google's mobile search results, with a top preference assigned to sites designed to guide users to content that has been optimized for their mobile device.

Google is also instituting another modification to their search results. This one is related to something they call “app indexing”. App indexing is defined as the process by which a visitor can jump immediately from a search result to a related Android application (For example, if a search result identifies a recipe from a food website, presuming you already have it installed – selecting the result would launch that recipe right within the associated app).

Google also said: “Starting today, we will begin to use information from indexed apps as a factor in ranking for signed-in users who have the app installed. As a result, we may now surface content from indexed apps more prominently in search.”