Possibly the best (and most succinct) explanation of designg in XP I have seen yet, from Ken Boucher on the XP mailing list. Whatever might be said about the signal-to-noise ratio on that list, there is still very good discussion going on there for those who can sift the wheat from the chaff.

(Ok I think I've exceeded the allowable number of quality metaphors in one posting, I mean who doesn't know the cream rises to the top when one is able to soar like an eagle above the turkeys?)