Cold and rainy weather has already washed out the game between the Mets and the Nationals at Shea Stadium as well as a doubleheader between the Giants and Pirates in Pittsburgh.
Saturday's fleece blanket giveaway in Pittsburgh was postponed as well, although parkas, balaclavas, and mukluks are available. The entire Pirate team was going to wear #42 today as was Barry Bonds for the Giants. I suppose they can wear it around in the clubhouse.
Update - Add the Angels and Red Sox to the list of postponements. They are scheduled to play Monday in a Patriots Day matinee that would start at 7 am PT. And you can also add Houston at Philadelphia and Kansas City at Baltimore to the list of game postponed.