These days more and more people are surfing Internet from their phones. Take a look at following graph. It shows number of monthly visits to googlestore.com from Android, iPhone, and BlackBerry devices over past 2 years. There were 277 visits in Sep, 2008. But in July of 2010, there were over 13,000 visits!
"Given this kind of growth, it makes sense for many businesses to set up a mobile device-friendly site. If you've been considering whether to create a mobile site, you may want to check out Mobile Devices report in Visitors section. You can see how many visits you received from each mobile operating system, how many pages they visit on average, how much time they spend on your site, as well as see conversion and ecommerce information," explains Google.