I've seen a lot of these from the bride's perspective, but not a lot from the guests'.
I was recently invited to a wedding of a long time family friend (26 years - we have known each other since birth). My parents just received the invitation which is addressed to our family. Just the 4 of us, with our names clearly spelled out. I would like the record to reflect that I do not live at home so this in itself is a tad insulting. (Really, they couldn't have bothered to ask me for my address for my own invitation?)
My boyfriend and I have been together 1.5 years and this friend has met my boyfriend. I understand people often don't invite +1 for cost reasons, but that doesn't seem to be a concern for this couple as they are having the wedding at a very fancy venue, or because the guest doesn't have a significant other, but that's not the case either since I clearly have one.
Is it ever appropriate to ask the couple if I can bring a plus one? The only people I will know at the wedding are the groom and my family....