UPDATE: March 15, 2015
Since writing this article, there's been a lot of speculation about what Google was going to do in regards to mobile SEO — but at the end of February, Google officially announced that they will be taking mobile-friendly sites into their search ranking criteria.
Starting April 21, we will be expanding our use of mobile-friendliness as a ranking signal. This change will affect mobile searches in all languages worldwide and will have a significant impact in our search results.
If you're struggling on whether or not to take a new approach to your web strategies and make the leap towards a responsive website then this just might be what you need to hear to move forward — Google has begun tagging sites that are responsive (aka mobile friendly).
We see these labels as a first step in helping mobile users to have a better mobile web experience. We are also experimenting with using the mobile-friendly criteria as a ranking signal. —Google
So What Does This Mean?
You'll slowly begin seeing Google implement "labels" next to sites on mobile search results for sites that are mobile-friendly so you know before hand whether or not it's going to be a pain to navigate.

What About My SEO & Search Results?
While Google hasn't explicitly said that they're going to take whether your website is mobile-friendly or not into mobile SEO and search results, it's an indication that this is a good possibility they are looking into implementing in the near future and here's why:
1.) In June of 2013, Google announced that sites that cause problems for mobile visitors appeared lower down in mobile search results.
The main problem/concern Google is talking about are sites that redirect to a mobile site.
The problem with redirecting to a mobile version of your site is that users can Google for certain information on your site, see the search result they're looking for and click the link. But often times instead of being redirected to www.example.com/page-i-want, they're redirected to m.example.com and can no longer access or find what it was Google listed. (This also a strong argument for going responsive. Content is much easier to access)
2.) Since there is an already existing penalty for "poor mobile sites" it only makes sense to reward sites who have a mobile experience that's easy to navigate.
After all, It's estimated that by the end of 2014, mobile internet usage will surpass desktop usage.
3.) Improving the Overall Web
It's pretty obvious that Google's a big proponent for making the web accessible to everyone and keeping up with current technologies and trends, so sites that help them in their goal are probably going to get better search results.
In relation to mobile friendly websites, Google said it will, "improve the mobile web, make your users happy, and allow searchers to experience your content fully.”
To help users determine if they meet the criteria for a mobile-friendly site, Google's created a Mobile-Friendly Test composed of the following criteria.
- Avoids software that is not common on mobile devices, like Flash
- Uses text that is readable without zooming
- Sizes content to the screen so users don't have to scroll horizontally or zoom
- Places links far enough apart so that the correct one can be easily tapped
Take the Mobile-Friendly Test Here
Did You Pass or Fail?
Congrats if you passed! If you failed, don't stress out. Google realizes that this is still a relatively new technique that takes time and resources to fully adapt to, so it's pretty safe to assume that there's going to be some time before they start ranking pages for search results based on whether your site is responsive or not. However, it is something that you should definitely take into consideration in the near future.
The Sooner the Better
Why not jump to beginning of the line and beat out your competitors with a responsive site, so if and when Google roles out their new ranking strategy, you'll be miles ahead of your competition.