Thanks to Fr. Juhl for passing along this insightful article about messing with Mass - from a Roman Catholic perspective, but very applicable on this side of the Tiber as well.

Money quote:

Setting aside the important underlying theological issues, we can see deeply rooted psychological motives behind the American priests who “individualize” the Masses they celebrate, placing their “personal stamp” on the liturgy. These priests play fast and loose with the rubrics of the mass, transform the “very brief” introduction after the greeting of the people, as authorized by the General Instruction of the Roman Missal, into another homily. Some even individualize the prayer of consecration, and in numerous other ways seek to make the Divine Liturgy conform to their own tastes and views.