It may still work for mods, but it seems that for we plebes there will be no more following of threads simply because we are curious.
So expect a whole lot of 'huh?' replies to threads where one is just curious. (Don't know if the 'notify' button on the replies is still valid, but that seems to now be the only way to express curiosity...)
You have to post in the thread for that option. I believe they are referring to the white envelope that is normally up at the top. That gives you notifications without having to comment in the thread.