Since Joe quoted the article at Nik's site, I will simply quote myself from that thread:
It would be interesting, I think, to see what Pius V actually wrote regarding his reasons for altering the Sign of the Cross. Nevertheless, while the article is interesting regarding the older Latin practice compared with the regular Greek practice, it doesn't definitively settle the matter for me. The Oriental Orthodox Churches have, to my knowledge, always used the same hand positioning as the Greeks (thumb, index, and middle fingers joined, with the ring and little fingers closed), but from left shoulder to right. This is because the Son of God came down from Heaven (forehead) to earth (somewhere around the belly button) to redeem those who stood condemned (left shoulder) and bring them to salvation (right shoulder).