Every "reply box" is now one set of code. That means all markdown boxes with a preview button have been centralized. This means possible bugs.
I found one already, will you?
Also, no round trips to server to get reply form html. Now reply forms are embedded in the current page render, cloned, then displayed. Should be must faster.
One more bug I know of in concerns to editing a nested comment.
All bugs should be fixed. Prove me wrong and get badged. :)