The excellent journal of the Society for Catholic Liturgy, Antiphon, has made available on the internet an interesting exchange between Fr. Pierre-Marie Gy, O.P. (who was critiquing Ratzinger's liturgical thought in The Spirit of the Liturgy) and Cardinal Ratzinger's response to Fr. Gy.
Here is that piece which comes from the recent 2007 edition of Antiphon.