how much?
depends on who you ask:
The official in charge of monitoring America’s $51 billion effort to reconstruct Iraq has estimated that $6 billion to $8 billion of that amount was lost to waste, fraud and abuse.
Stuart Bowen, the special inspector general for Iraq reconstruction (SIGIR) for the past eight years, gave that estimate in an interview with the Center for Public Integrity on Monday, shortly after releasing a new summary of his office’s many grim discoveries since it began work in in 2004.
In Friday’s report, Bowen said the exact funds lost to fraud and waste “can never be known,” largely because of poor record-keeping by the U.S. agencies involved in the effort. These include the Departments of State and Defense, along with the U.S. Agency for International Development.
According to the report, auditors repeatedly found that the State Department and Defense Department failed to properly review invoices from government contractors, often approving billions of dollars in services without checking if costs were accurate or efficient. “I think the consistent theme throughout our eight years of oversight work has been the inconsistent availability of records and information on contracts and costs,” said Bowen, a former Texas lawyer.
Bowen said his efforts were hampered from the outset by the ineffectiveness of a clearinghouse created in Iraq for government departments to submit reconstruction bills and contracts for review and oversight. Known as the Iraq Reconstruction Management System, the system was often ignored, with the result that nearly a third of all the contracts could not be monitored adequately.
I suppose if you blame the Dems they'll say $6 billion while the Republicans will say $8 billion, and vice versa.
personally I blame a lack of respect for their cultural history by the youth of Iraq:

c'mon, all those blocks and not one ziggurat built?