We haven't told our parents yet, as the wedding is scheduled for 2013, but we already expect my side of the family to have a fit over the cost of the trip. Most of them are people we don't want there, so we feel it works to our advantage. It saves me the awkwardness of explaining why they are not invited. My parents may not be there, due to the cost, but I'm not close to them and will not be the least bit bothered, one way or the other.
I think it is so different for each person. Consider whether you cannot imagine getting married without your parents there, or whether you cannot imagine getting married at home. For me, it's definitely the latter.