stupid question by a genuine seeker of knowledge?

Every one decides for themselves. I'm gonna take my husband's surname and combine it with mine (hyphenated). =]*X

It's completely up to the partners. I've seen couples who've done it 4 different ways--the 3 you've mentioned and a combined last name that was formed from both last names (e.g., Van Halen + Vedder to get "Van Vedder.")

In a "traditional" marriage (man with woman) the woman doesn't always take the name of the man. In fact, I've known a man or two to take the name of the woman. So...go figure. It's differs from marriage to marriage. In my case (I'm a man marrying another man) I would hyphenate our last names.

it is up to the couple..

Although I am not and not planning on getting married any time soon, I do not intend on changing my surname. And I wouldn't want my "husband" to either.

It's the same as in a straight marriage, it's completely up to the people getting married.

They hyphenate most of the time.

It depends on the person, they decide for themselves