I know, a few of us that were in chat last night did tests. There is a visible diffence to the the title of the thread IF you are reading posts from a specific forum (ie Main, General Chit Chat, etc) AND IF you hit "refresh" after exiting the thread.
There is no visible change to threads when they are read from the "whats new" section. I *think* a lot of us use this as it's a "one stop shopping" place so to speak.
I really would like that feature back.