http://www.usccb.org/liturgy/girm/bul4.shtml
"We are called to listen attentively as the reader, deacon or priest proclaims God's Word. Unless one is unable to hear, one should not be reading along with a text from a missal or missalette. Rather, taking our cue from the General Instruction itself, we should listen as we would if Christ himself were standing at the ambo, for in fact it is God who speaks when the Scriptures are proclaimed. Carefully following along with the printed word can cause us to miss the gentle voice of the Holy Spirit, the message that the Spirit may have for us in one of the passages because we are anxious to 'keep up,' to move along with the reader."
http://www.usccb.org/liturgy/innews/798.shtml
"Its clearly preferable that the word of God be clearly heard by all who participate in the liturgy, for "In the hearing of God's word the Church is built up and grows". (GILFM 7) For this reason, the printing of readings and presidential prayers in participation aids is discouraged, unless other circumstances make it impossible for the word to be effectively proclaimed. Even in these instances, however, it is preferable that steps be taken to assure the effective proclamation of the Scriptures rather than resorting to providing a "read along" text to the members of the assembly."