I'm with Anthem Blue Cross in California. In 2011 they spent 79.9% of premiums on actual medical expenses and due to law changes had to issue a refund for 0.1% This year they raised premiums by 22%.
Various administrative expenses are hidden all over the place. eg the cost of an appendectomy also includes the cost of recovering the money charged.
The problem with the US healthcare system isn't any one part. Every single part is broken in some way, with the interoperations between them compounding to make the problem worse.