Figures from IDC show that Android tablets took 44.6% of the market share in the fourth quarter of 2011. This is up from 32.3% in the previous quarter. The increase in market share was due mainly to Amazon's Kindle Fire which accounted for 16.8% of all tablet sales. This figure is pretty impressive given that the Kindle Fire is sold only in the United States, and its appeal to worldwide customers is limited given that the Kindle Fire does not access the Google app store, but its own Amazon Appstore which only caters to US customers.
Apple's market share in the fourth quarter of 2011 declined to 54.7% down from 61.5% in the third quarter.
When you add the 3.5% market share of the Nook to the 16.8% market share of the Kindle Fire there appears to the a fairly large demand for low cost 7-inch tablets. The Nook like, Amazon's Kindle Fire is not marketed worldwide. Other Android manufacturers could exploit this and fill the demand in countries were the Kindle Fire and Nook are not marketed and supported.
With the launch of the new third generation iPad in the first quarter of 2012, I would expect Apple to regain some of its lost market share. The decision to continue production of the iPad 2 in 2012 and a reduction in its price to US$399 for the WiFi only model should also help.