Is wearing a long strapless dress to a wedding a bad idea?

Fashion is different in different parts of the country, and I'm from the midwest, so keep that in mind with this answer: I think you could get by with the strapless part if you're not showing too much and you wear a little jacket or sweater, but the full length, in this fabric, is really only appropriate for a formal or evening wedding. You don't want to be more formal than the bridesmaids.