I think this works in the chat but don't see the use of it in a group. I thought I wouldn't like it when it was announced for the chat but now it's nice to see a "seen" message. This kind of thing is a pressure to engage faster since you know when the other person has read something you sent to them in a one-on-one conversation. Then again, as others have mentioned, how can FB know if I've seen something or not. Surely, we'll have eyeball-following cameras in everything soon.
