I dislike it too, for its arm’s-length academic treatment of personal relations. In fact, it triggers my gag reflex, so I never use it myself. I can see why sociology and psychology need such a term (and they do define it differently from the popular meaning), but it sounds like clinical jargon to me, just like referring to a first-time mother as a “primipara” and a baby as a “neonate.”
“Want to see my neonate?”
“Your neonate is adorable.”
“What did she name her neonate?”
“How do you do? I’m a primipara, this is my significant other, and here’s our neonate.”
However, I know many people who use “significant other” to refer to their, um, (?) their common-law spouses, and not just for gender neutrality. In fact, I most frequently hear it in a heterosexual context. After 30 years together, the couple might feel a little old to say “boyfriend” and “girlfriend,” and “partner” sounds a little . . . I don’t know, coldly pragmatic perhaps (“the person I do it with”) . . . and everybody knows they’re never, ever going to get married. I don’t know what I would say in their place, except maybe just—“This is Sam.”