I think that adding a quick reply box would make replying to posts a lot easier and would also be beneficial to dial-up users, since when posting a reply to a topic they would have one less screen to load.

 

 

 

Something like http://www.phpbb.com/community/viewtopic.php?t=230887 would probably work nicely. Here's a screenshot of what it would look like:

 

 

 

This happens to be on the blacklist for suggestions so unfortunately I have to lock it. I believe part of the logic for not having it is because it would make it that much easier for users to post without thinking since the box is right there.