From reading the article "Bust Out the Soap, It's the Simic" on the MTG website, the last creature in the little game in the article is obviously a preview for Coldsnap and, from the text revealed when you click the link labelled "More", that poison counters will be making a return in Coldsnap.
http://www.wizards.com/default.asp?x=mtgcom/daily/mc41Scroll all the way down to the bottom. It's the last entry in the game.