Currently, the process of reading comments for a question/answer goes something like this:
- Read the 3 or 4 top rated comments
- Click the "add/show more comments" link
- Start at the top again, reading comments you think are new, tring to figure out which ones aren't
This reminds me a lot of the old Microsoft Office Intelli-menus, where an essentially random set of menu items would surface to the top, and the rest would be hidden. Upon clicking a little chevron at the bottom of the menu, the rest of the menu would appear, but instead of appearing at the bottom like you'd expect, they appear scattered throughout the menu you just looked at. Just like in the current StackOverflow implementation, you have to start reading back at the top again and scan back through to find new stuff.
It would be better from a user experience standpoint to just show the remaining comments at the bottom when "show more comments" is clicked.