Nice job, James, on covering AAA...it's an extremely valuable tool, not only for transactional processes, but for manufacturing. I had one manufacturing client that was losing millions of dollars a year because their "standards" for identifying machining defects, staining, blemishes, etc. were all victims of very low agreement. Companies can save themselves a lot of trouble if they learn this skill.
I do want to suggest, however, that Measurement Systems Analysis, whether it's Gage R&R (for continuous metrics) or AAA for discrete categorical metrics, should be used throughout DMAIC. My own approach is admittedly a little different (see "A DMAIC Makeover" in QP Dec 2008)...I insist on a baseline in Define. Even if you wait to do it in Measure, though, you can't just do it for your baseline data and then not use it for all the different process measures you find in Measure and Analyze. While most measurement error will generally have a minimal impact on SPC charts, it is absolutely vital in more distribution-dependent tools such as hypothesis testing, regression and DOE.