The New York Times has a lengthy story today -- in the business section -- on "the new wariness of collectors, both public and private, to buy or exhibit works that do not have the most rigorously documented history." According to the story, "antiquities experts say the mood in the art world turned sharply with the 2002 conviction of the prominent New York art dealer Frederick Schultz. He was found guilty of violating the 1934 National Stolen Property Act by conspiring to receive stolen Egyptian antiquities." Archaeology magazine had a comprehensive series on the Schultz case here.
UPDATE: Lee Rosenbaum comments here.