Sometimes we have to build a FallingWater. --KyleBrown
This is a tough one. I've done a lot of R&D software, and in some ways really have advanced the state of the art. Sometimes, however, the people I was doing it for had in mind satisfying their customers on a timely basis. Sometimes the advancement goal helped in satisfying the customers, but sometimes it got in the way.
XP, of course, focuses on the business value as defined by the customer. If my R&D projects had been done Extreme, I'd have had to convince the customers to invest in state of the art, or I'd have had to step back from some of the grander goals.
Many objections to XP seem to center on whether we are "against" doing cool things. Of course we aren't: we're against doing things that whoever is paying you doesn't want done. And if your job is to mess around trying to advance the state of the art, not all of the XP dicta may apply to you.
But, having worked both sides of the street, I think that many of them do. Perhaps we should explore how XP applies to R&D. Then again, perhaps not.
The SecondSystemSyndrome also puts developer motivation ahead of customer needs.