Recently, on several different occasions, I talked to a few different folks who had been married much longer than I - 30 years or more - and who were convinced that addressing packages or letters to "Mr. and Mrs. [Husband's First Name only] Last Name" was the "correct and proper" thing to do.
I don't know where they got their information, but I wish folks would recognize that styles and preferences change. I don't know if there are any hard and fast rules about what you're "supposed" to do, but I'm pretty sure the preference is up to the person whose name has been voluntarily changed - especially in the intervening decades when it was assumed that women would change their last name upon getting married.
Of course, it's not always possible to know said preference. Last Christmas Ed and I got a Christmas letter addressed to Ed Szetela and Michelle Solomon; the folks who'd sent us this letter were friends of Ed's parents, whom I've never seen before, and possibly won't see them again, or for a very long time. It's impossible to know if a woman will change her name after marriage without asking her.
It's true that I was eager to change my last name to my husband's after we got married; it was a chance to create a new identify of my own. I love my parents and my family a lot, but at least in name, I want to be associated first with my husband and our family.
However, I did not change my name to "Edward," so addressing a letter to "Mr. and Mrs. Edward Szetela" seems to imply that I've also changed my name to Edward, which I have not done (yet). Edward is a very nice name, but I plan on keeping "Michelle" until such time as there's a good reason to change it.
What it comes down to is the need to get with the times. "Mr. and Mrs. Only-Husband's-First-Name-and-Last-Name" is no longer the style. Or, dare I say, the preference of anyone I know who's been married within the past 10 years.