Android had 22% of the tablet market in Q4 2010

"The latest research published by market research company Strategy Analytics, has found that Android’s momentum is not limited to mobile devices but is also showing big gains in the tablet market.
According to the research during Q.4 2010, 22% of the 10 million tablet devices that where shipped ran on Android. Overall the market grew by 120% sequentially with Apple maintaining it’s leading position with 75% of global market share."

Source:  Data from Strategy Analytics, reported by MobiADNews, 27th February 2011