I couldn't possibly subscribe to using "extreme programming" for the very simple reason that it's a really stupid name! It conjures up images of banging out uber-complex C++ code while snow-boarding down the virgin snowy face of a desolate mountain (on one leg), and undertaking negotiations for a multi-trillion pound investment program (via a leading-edge satellite phone) in-between fighting off hoards of rabid bears.
The other reason is that "extreme programming" basically translates as "doing your job properly". It is nothing more than that.
I've been "doing my job properly" (or at least trying to) for years, and I don't need someone to come along and stick a label on how I work. I don't have a "methodology" for "doing my job properly". Unless you call the combined ideas of common sense, planning, attention to detail, and quality a "methodology".
"Extreme programming" (I cringe every time I write that) is just like UML and SSADM (remember that?) and Yourdon (showing your age now, eh?), and a multitude of other methodologies and ideas for how we should do stuff - ie - it's just a way of selling books!