My workaround to Address Book's limitations was to create
three cards: one for each individual, and as recommended by others here, noting the partner's name in the spouse field. But then I create a third card that combined the 2 names - doesn't really matter which name field you use, put it all in one field.
I did it this way for a couple of reasons. Invariably, each person is going to have some differing info even though they share an address, such as emails, notes, cell phones, etc..., this way I can have that unique info for each individual without a lot of custom fields on one long card, trying to figure which info is whose, etc....
Then the third card I use for contacting them as a couple - holiday cards, invites, etc... Email headers, prints on labels and envelopes as you'd (or even better, they'd) expect. I simply add a unique word like "christmascard" in the note field for the couples "Bob Smith & Jane Doe" or "Mr. & Mrs. John Q. Public" for instance, create a smart group based on having "christmascard" in the notes field and can call up all those marked cards as a group for labels or whatever. (Conversely, you would not put "christmascard" in that couple's individual cards)
And of course searching on any of the names brings up all three cards if needed.
This idea can be carried even further by adding more than one unique word to the notes field which I seperate with returns...like family, jokeemail, buds, cousins, well you get the idea. Smart groups are great, puts "related" people/addresses all in one spot for easy use.
Hope my 2 cents helps.
Pat Gallagher
XServe Mac OS X (10.4.3)
XServe Mac OS X (10.4.3)