I have managed to persuade my major client, Pick 'n Pay (the largest (by market share) supermarket chain in South Africa), to try some of the extreme practices on one of their projects. I had only read about XP, pointed some people at it, and had them report happy eXperiences - sufficient to give me the confidence to push pretty hard for XP. The organization suffers many of the "usual" problems of constantly-changing requirements and priorities, poor delivery, too-long gaps between releases, so XP seemed like a very good fit.
The first project to attempt some of the extreme practices was scheduled to take four programmers, plus a team leader three months. They lost the most senior programmer (who also knew the business environment the best) before the project got under way. A blessing! He was (and remains) very resistant to any new ideas. They completed the project a month ahead of schedule. At that, they were using only a small subset of the extreme practices - PairProgramming, UserStories, and a little (when I could convince them) UnitTesting.
Now the programmers involved, and Pick 'n Pay development management are pretty convinced the XP is right for them, and another project (with entirely different staff) is taking a lot more of the practices a lot more seriously.
I am still having a great deal of difficulty getting the organization to put a Customer on the team full-time, and also in getting a decent FunctionalTesting culture entrenched.
I did not in any sense convince them to drink the whole cup of coffee in one go - but they're drinking it a sip at a time. (Did I mention it is a Java shop?)
I will try and report progress and use of XP on these (and any other) projects as they progress.
-- MikeMorris