Totally not accurate, but if you assume a 40/7 ratio of iPad to iPad2 installed base and about 18 million original iPad's out there, you get over 3 million iPad 2 sales over the past two weeks.

The entire US PC industry (including Apple) is only about 6 million units/month, it took the original iPad 80 days to reach 3 Million in sales.

http://www.engadget.com/2011/01/14/idc-and-gartner-us-pc-sal...

http://www.appleinsider.com/articles/10/06/22/apple_announce...