Just recently some states have begun cracking down on this. Over the past couple snowstorms, an individual State Police officer in New Hampshire issued hundreds of tickets and many other warnings. In NH it is a $500-$1000 fine in addition to the humiliation of the State Police posting a picture of you clearing your snow on Twitter.
Even though this seems excessive, NH has had a lot of issues regarding snow and ice on roofs, as I'm sure many northern states have. This is a scenario where it only takes a few seconds to prevent a chunk of ice from killing someone so it makes sense to police it pretty militantly.