http://store.steampowered.com/news/24155/The way I read the news, was that you could post a REVIEW but not a RATING.
I think a Rating is the thumbs-up or -down part, but I just looked at one of my old reviews of a game I got a free key for, and it still has the thumb attached. Just tried to write a fresh review for a different game that I bought on Steam, and it still had the voluntary check-box for if I received the game for free.
Tried another that I had on a Bundle, and it still gives the option to select a Thumb.
So, not sure. Have not actually tried submitting either of those reviews, so don't know what would happen there. Maybe my steam client needs to update? Or maybe it is transparent to the user, but as Nenjin says, they just are not counting it on the back end?
Certainly the steamspy data as well as the data published by steam directly and information from individual developers backs up the fact that these reviews are no longer being "counted".
But it seems like old reviews are not vanishing, can still be read, and new reviews with Thumb "ratings" can still be posted. So, anyone who cares enough to read reviews can still see it, and anyone just looking at the initial rating before reading more about the game will get the filtered data.
Seems totally reasonable to me.