I don’t care what you sell, who your customer is or how small a business you have. I am talking to you.
Take a look at these statistics:
    • 58 percent of all U.S. consumers already own a smartphone.
    • 50 percent of mobile Web users now use mobile as their primary or exclusive means of going online.
    • No single screen size (desktop, tablet, mobile) has more than 20 percent market share.
    • 61 percent of users have a better opinion of a brand when it delivers a good mobile experience.
    • 90 percent of users move between devices to accomplish a given goal or task.
    • 26 percent of all email is opened on a mobile phone.
    • 80 percent of smartphone and 81 percent of tablet owners use their device in front of the TV.
    • 80 pecent of consumers plan to conduct mobile commerce in the next 12 months.
    And the two most damning bits of reality check stats on this topic:
    • 61 percent of mobile users are likely to move onto a competitor’s site if your page isn’t mobile optimized.
    • 57 percent of users say they will not recommend a business with a poorly designed mobile site.
If you don’t invest another minute or dime on marketing in 2013, you absolutely must see the urgency and importance of making your website mobile friendly. I don’t care if your primary customers are 85-plus; they and their influencers (typically their children) are using mobile.
Hopefully by now I don’t have to convince you how vital the Web is to any buying decision. Whether you sell toothpaste, a luxury vehicle or a quarter of a million dollar piece of medical equipment, your consumers are doing their research and pre-shopping on the Web. Studies show that in many cases, they’re almost 70 percent done with their shopping phase by the time they reach out to you by email or phone. The higher your price tag, the more time they spent on the Web before actually making contact. So if you sell a high-ticket item or service, you’re taking a huge risk by not following this advice.
Retailers are also a high-risk group. Restaurants seem to be a category that is really missing the opportunity here. I travel quite a bit and rely on websites like Yelp and Open Table to help me find nearby places to eat in cities I’m visiting. If I read a great review and then click on the View Their Website link and it’s not mobile optimized, I keep looking because I can’t get the information I need before making that decision.
In fact, I might argue that many retailers only need a mobile site and could, if they had to for budget reasons, forgo the desktop site. Ideally, you’d have a full website that is optimized for screens of all sizes, but in some cases, mobile is so critical that if you only have the money or time to do one, mobile would be your best choice.
Don’t fall into the “I don’t need my website to be mobile optimized, I just need an app” trap. Apps are great tools but they serve a completely different purpose. Apps are for people who already know who you are and, most likely, are already your customer. Business-related apps are about providing clients with access to information and convenience, not for someone who’s never heard of you.  
Every day you delay this decision costs you customers and money. Ultimately, if you don’t update your site to be mobile-friendly, you will be viewed in the same way we view businesses with no Web presence today.  
Absolutely irrelevant.