I don't initiate hand-holding during the Lord's Prayer (probably because I'm an introvert), but don't mind it at all.  I'm okay with it as a general Mass posture.  I am a bit bothered when I see it happening only among family and friends.  This ritual would suggest unity among all believers as daughters and sons of "our" Father.  If only some, and not all, do it, then it seems to be a "counter-symbol."