The New York Times reports that substantial numbers of artifacts repatriated to Iraq have gone missing. See http://www.nytimes.com/2010/09/08/world/middleeast/08iraq.html?hp
A witch hunt ensued after the looting of the Iraqi National Museum that led to the repatriation of many artifacts, some of which at least probably never came from Iraq in the first place.
In Saddam's Iraq, Baathist leaders sometimes traded in stolen antiquities without interference. It is unclear whether the artifacts that are now missing have shared a similar fate or have just been temporarily misplaced.
Last year, one of the Iraqi Prime Minister's relatives was detained in Dubai with Sumerian artifacts he was allegedly trying to smuggle to the United States. See http://www.culturalpropertyobserver.blogspot.com/2009/10/iraqi-pms-relatives-are-said-to-be.html That story quickly disappeared from view, but perhaps this news item will prompt some additional investigation.