This was kind of handy, but now it's a drag. I'm on a slow connection and I just had to click post 3 (3!) times. I didn't see a way to turn it off, do we really need it?
It's useful in discussions, but I also think one notification per new post is enough…
Conceivably in the future a thread could get so hot that you could never get in on a slow connection!
I'm actually annoyed at it in general. Normally if you post right after someone you can still get "credit" for it, but with the warning sometimes I feel like I should delete because it's already there in about as good words, and I know that everyone will know that I should have known about the previous post.