The House Committee on Oversight and Government Reform is taking up the Blackwater scandal today. You can watch the hearing on their website.
Much of the discussion has been about about accountability, standards and efficiency. A new angle, being developed in this hearing, is that private contractors like Blackwater aren't effective in the sense that they harm, rather than help, military counterinsurgency campaigns. When contractors are running amok, it's harder to win hearts and minds.
P.W. Singer of the Brookings Institution just recently a paper on this issue. Definitely worth a read.