A recent info-graphic from Get Satisfaction (an online community platform for businesses) shows the importance of responsive website design. No longer can companies afford to pursue just a mobile or desktop web solution. Get Satisfaction thinks sites should be responsive for each screen size (including your TV!), and they have some statistics to back this up.
While the majority of Get Satisfaction visitors come from a mobile device, more new visitors discover the site while using a desktop computer or a tablet. There are also more referrals from desktops and tablets than smartphones. They predict that mobile internet usage will eclipse notebooks and desktops in 2014.
Get Satisfaction also highlights the importance of responsive design. They estimate that "by the end of 2013, there will be more mobile devices than the world's population." They note that 90 percent of users make use of multiple screens. This could be interpreted as computers with multiple monitors, but it could also include a notebook/desktop and tablet combination. Having a more fluid and responsive web experience is extremely important for e-commerce, as 67 percent of online "shoppers start on one device, then continue their purchases on another."
This is certainly not the first info-graphic that highlights the importance of mobile optimized sites and responsive design. But, it does show that the notebook/desktop is still an important piece of screen real-estate; it has not been completely replaced by mobile devices, but rather it complements them. It's a reminder to companies that their websites need to scale well for all screen sizes, and provides the best possible user experience.