There was a 3 day series in the Washington Post earlier this month, exposing them. Here are some links from Ethan_Allan's post on them:
TODAY'S ARTICLE - HOW A BID TO SAVE A SPECIES CAME TO GRIEF
http://www.washingtonpost.com/wp-dyn/articles/A13933-2003May4.html
Cover page for all articles is here: http://www.washingtonpost.com/wp-dyn/nation/specials/natureconservancy/
BIG GREEN : Inside the Nature Conservancy Nonprofit Land Bank Amasses Billions (thread)