I haven't read any more on this yet, but this abstract caught my eye: "A critical evaluation of oncology clinical practice guidelines", to be presented at the 2012 meeting of the American Society of Clinical Oncology (ASCO).
Summary: Researchers reviewed 168 clinical practice guidelines for treatment of 4 common cancers (breast, lung, colon, prostate).
None (i.e., 0) of them met IOM (Institute of Medicine) standards for reliability or trustworthiness.
I'm just glad mandated use of practice guidelines isn't being imposed by ObamaCare. Oh, wait...