“We had more than 425 million mobile monthly active users in December 2011. In 2011, mobile usage of Facebook increased in markets around the world, including major developed markets such as the United States where smartphone penetration grew rapidly… Improving our mobile products and increasing mobile usage of Facebook are key company priorities that we believe are critical to help us maintain and grow our user base and engagement over the long term. We expect consumers around the world will continue to increase the amount of time they spend and the information they share and consume through mobile devices.” – Facebook IPO statement (February, 2012).
So now you see how important to have website design that could fit all devices (pc, smartphones, tablets,and laptop).