Silicon Alley Insider has posted a chart showing the comparative results of reported iPad usage from November 2010 to the current month of May 2011. As you can see from the chart above, an overwhelming amount of people spend a majority of their time on Apple's tablet surfing the web -- most of those people presumably using Safari to do so.
After web browsing, which came in at 36%, emailing, Facebook, and Twitter usage on the iPad came in second place at 23%. Social networking was followed by "other app" usage at 21%, and after that watching videos and gaming virtually ti