Robert blogged about the new beta release of the patterns & practices Acceptance Test Engineering Guidance document. I have had a chance to do a quick read now and I have to say I am impressed. If nothing else it gives great comparative look at waterfall and agile methods for delivery, and a review of many types of acceptance testing.
As with many of the p&p documents it is not exhaustive in what it covers, but what it does give is an excellent and detailed starting point for you to make the decisions that are right for your project. It does not give all the answers just most of the right questions.