From a tablet market share snapshot
Though Apple's iPad shipments grew in the fourth quarter of 2011 -- to 15.4 million versus 11.1 million in the third quarter -- it nonetheless lost market share. In the fourth quarter, it held 54.7 percent of the worldwide market, down from 61.5 percent in the third quarter.
Amazon shipped 4.7 million Kindle Fires in 2011, enough to boost the company into second place behind Apple with 16.8 percent of the worldwide market.
[…] Here's IDC's chart: