I think physical keyboards should come with a "post/submit" key separate from the "newline" key, like the iPhone keyboard does.
Why? Does this solve a perceived usability issue? It's just going to confuse its users.
When in a multiline text field, pressing Enter should add a new line. (If comment fields where single-line text fields, however, I'd understand the change.)
I don't quite like the hitting Enter to post. Though, I can deal with that. I do, however, like how we can essentially edit our posts. That was something that always frustrated me with Facebook comments.
It's horrible for usability. If you don't have JavaScript on, you lose the ability to submit comments entirely. Not that Facebook was very usable with JS off to begin with, but still.
I'm not one to complain about UI changes, but I truly think they'll need to tweak this. In fact, it should be the reverse IMHO. Shift + enter= submit and enter= carriage return.
I was having the exact discussion with a friend yesterday of what the default behaviour in real time should be.
My friend was of the opinion that it should be Enter to post and "Shift+Enter" to add a new line. What facebook did today basically.
My stand was the oppposite. Shift+Enter for a new comment and enter for new line.
The reason being that even if I press enter thinking it would post my comment, the error handling (forgiveness to the user) is minimal and I can either click the button or be informed that to post I need shift + Enter.
However if I do it the way facebook does and press enter thinking it would take me to a new line without me realising that I posted a comment that is half of what I wanted to say.
Lesson: Let you interface be forgiving and give it priority over simplicity.