I can't seem to find it, has that functionality been removed?

Some videos have prompted long and informative discussions spanning days, but right now there's no convenient way to see when someone replies to your comments. I suggest that when you post a comment, you can check a box that'll send you email notifications when someone responds

I tried to post a follow-up to http://www.videosift.com/video/Ron-Paul-on-the-Federal-Reserve#142832
but it was stuck at "processing your submission"

I think it's something to do with size, later I submitted a small post, then edited it into original post, and it worked

How about adding Slashdot-like ratings to comments? That would encourage people to add useful information/descriptions in comments even if nobody asked for it specifically.