If you are interested in device class and OS version statistics, I’ve compiled a list of recent articles:

• iOS device and OS version stats from Instapaper 3.0 2011-03-24
• is it worth supporting iOS 3 in 2011? 2011-03-20
• What proportion of all iPhone owners use iOS 4.x today? 2011-01-18
• 61% of iPads already running iOS 4 2011-01-07