The national enquirer may have only been "successfully sued" once - i.e. losing a court case. But they've been forced to settle out of court MULTIPLE times for slander and other reasons:
http://search.yahoo.com/search?ei=utf-8&fr=ytff1-sunm&p=national%20enqui...
All you have to do is type National Enquirer Settlements
In otherwords - the Enquirer is not as "fact checked" as Thom believes - otherwise they wouldn't have to repeatedly give retractions or out of court settlements.