Great feature article on Gamasutra about rapidly iterating on a prototype.
While our studio, Boomzap Entertainment, is agile in the simplest definition of the word ("can move fast, is flexible"), we don't follow Scrum, XP, or any of the popular frameworks. Instead, we've tweaked a process that works best for our indie studio for the past five years -- a process I like to call "quick and dirty prototyping", though no one else at Boomzap refers to it as such.
Too many teams get lost in the labels and terminology and miss finding what makes sense. Good processes, no matter what the source, should lead to similar common sense practices. For example, I loved seeing the cost-of-change curve figure. That's the same curve that XP-ers use to justify the value Test Driven Development.