Three things I miss

[mdk]

keyboard shortcut for quick-reply (used to be alt+S)
video tags/youtube tags
auto-URL link

[Lucius Cypher]

I think the Alt+S thing only works on certain browsers, because even before the crash I couldn't quick reply on Firefox, but I could on Google Chrome.

That being said, it was a handy feature when I was using Chrome and had to shoot out posts.