We've covered a lot of ground in the last hour! Some of the XP practices are in use today by the mainstream development community; ideas such as increasing customer involvement have long been seen as important. It's the extreme aspect of these practices that makes XP a highly flexible development approach.
We also learned how the synergy of the practices is what makes XP work; the weakness of a given practice is mitigated by another.
Now we're ready to learn how to lead an XP project!