A new report from the USGS describes the history of rare earth production in China compared to the rest of the world, and the role of government policies. It's only 15 pages but it offers a much more detailed understanding of the recent restrictions on exports than I've read elsewhere.
"The volume of China’s rare-earth output as a percentage of total world output increased to more than 90 percent in 2008 from 27 percent in 1990. During the past 15 years, China has supplied more than 80 percent of the world’s rare earths..."
World-wide concerns about the supply of these elements for modern technology has set off a global rush to find new deposits or re-open old ones, and to find ways to recycle REE's from electronics.
Ref: Tse, Pui-Kwan, 2011, China’s rare-earth industry: U.S. Geological Survey Open-File Report 2011–1042, 11 p., available only online