I think it'd be good to have a reply field at the top and bottom of the comment list. The top one for when I want to angrily fire off my very important opinion without bothering to read through the whole comment list to see if anyone else has already angrily fired it off, and the bottom one for when I've finished reading all of the existing comments and have synthesized a well-considered and balanced opinion that accounts for all of what has been said so far (never used).