Per, Michelle Arnold (copied from her answer to this question, on Jan. 17, 2005):
"In the United States, the norm from the General Instruction of the Roman Missal (2002) is as follows:
In the dioceses of the United States of America, they [the congregation] should kneel beginning after the singing or recitation of the Sanctus until after the Amen of the eucharistic prayer, except when prevented on occasion by reasons of health, lack of space, the large number of people present, or some other good reason. Those who do not kneel ought to make a profound bow when the priest genuflects after the Consecration. The faithful kneel after the Agnus Dei unless the diocesan bishop determines otherwise.
With a view to a uniformity in gestures and postures during one and the same celebration, the faithful should follow the directions which the deacon, lay minister, or priest gives according to whatever is indicated in the missal (GIRM 43).
In short, in the United States, unless there is some good reason why people are prevented from kneeling during the Consecration, they should kneel. If they stand, they should make a profound bow when the priest genuflects following the Consecration. Lack of kneelers is not a sufficient excuse for not kneeling; it is only an indication that kneeling is going to be uncomfortable, not impossible. As for the unity question, the primary responsibility is to be in union with the liturgical rubrics set forth by the Holy See and the local bishops conference, as the GIRM indicates when it qualifies following clerical instructions as to posture by saying that the postures mandated must be in accord to the missal.