I started a new contract this week, in a group that is using XP merged with Alan Cooper's Goal-Directed development (c).
I must admit that it's very refreshing coming into an office with multiple teams, and hearing people having standup meetings, talking about Stories and acceptance tests, etc. There seems to be a real sense of buy-in from this development group for agile principles and practices. It's also gratifying in the sense that I was brought in to do an XP presentation at this client a little over 2 years ago, and I can see tangible results of that work!
This group has for several years now worked on many smaller projects with only 1-3 programmers. What's different about them is that they have almost always had an interaction designer work directly with each team, and this seems to have made a significant positive difference in the quality of the systems. The ID also acts as a tester for the application, although some of the larger systems have testers as well.
At any rate, I'm intrigued by the way they have consciously merged XP with Goal-Directed (c) development in a way that seems to use the best of both worlds. As I understand Goal-Directed (c) (and Alan Cooper's rants about XP), it suggests doing Big Interface Design Up Front. This development group, from what I've seen so far, does Medium-sized Interface Design Up Front and tweaks the interface during development based on Customer feedback.
It seems to be an interesting mix, and I'll keep my eye on it over the next month that I'm there.