There was a message in the WI DNR website stating it is up the localities as whether or not to open early. I saw a few counties down south are open now such as Green, Lafayette and parts of Dane among others. Many of the posts I have read where people are sledding in these areas are being told by others no matter what the state of WI does not open until the 15th. Unless specified I think this link clears in up a little.
http://dnr.wi.gov/news/DNRNews_article_Lookup.asp?id=1290
http://dnr.wi.gov/news/DNRNews_article_Lookup.asp?id=1290