Basically, now you can do everything that you can in a regular post, in Quick Reply now. Smilies, add YouTube videos etc. The only thing I can think of that you can't do that you can in a regular post is embed videos from places other than YouTube.
I found it frustrating to be halfway through a post in quick reply, and then realize, crap...I meant to add a trailer. Then cut everything and paste it into a regular post, so this code is sweet for me.
BTW, if there's functionality we don't have here that you'd like to have, there's probably a code for it, so let me know.