When embarking on Agile, many teams start with Scrum. Sooner or later, they inquire about XP. Is there one 'right' way of implementing Scrum and XP? Do you 'have' to do both?
This article by James Shore does a great job of summing it up. He says "Scrum is easier and less threatening than XP, so I see a lot more people starting out with Scrum. On the downside, the teams that start with Scrum tend to struggle more than the teams that start with XP. The XP teams experience more pain starting out, but then get to a high performance state within the first year."
As Agile evolves, and as Lean Startup enters the picture, I am sure of only one thing, that people will continue to debate this topic.
For me, I can say that I have seen successes both small and large when a team implements either one of Scrum or XP, and also success when they implement both. It's not so much that you go through the motions, but rather that you understand why you are going through them and make them meaningful for your team.