1. People talking about finding out the "gender" of their unborn baby via ultrasound.
No. Ultrasounds do not show anyone's gender. They show indications of one's sex. As we were taught in intro to sociology: You learn gender, you have sex. (A particularly funny choice of phrasing to 20-year-olds at a Christian college that forbids premarital sex.)
Is the gender you're imposing on them going to match its sex? Most likely. But not necessarily. Will a baby care that she's in a pink tutu when she really wants to wear blue overalls? No, but putting her in a tutu imposes the expectation of feminine traits on everyone around that baby, making it that much harder for her to express herself in any contrary ways as she grows up.
You'll have plenty of time throughout the kid's life to enforce gender roles on it, at least let it have the first nine months in the womb without that.
2. Addressing a couple as Mr. and Mrs. HisFirst TheirLast, or a woman as Mrs. HisFirst TheirLast.
I'm not even talking about last name choices (you've already read my thoughts on that). Even assuming that the woman in a hetero couple has taken her husband's last name: she continues to retain her own first name. Mrs. HisFirst TheirLast completely erases her identity as anything but His Wife. He can divorce or be widowed and remarry, and his new wife will also be Mrs. HisFirst TheirLast. It's all about her relationship to him.
There's a reason that traditional "etiquette" uses this as the proper address for a married woman. It's derived from a time when being married to a high status man was the pinnacle of achievement for a woman. Called a woman Mrs. Bob Smith would be akin to referring to her as Dr. Smith - an acknowledgement of her status in society being determined by her marriage.
It's also related to the concept of coverture. She didn't need her own personal identity, because legally she was the same as her husband. Women at times in the not so distant past had no control over their own assets and income, everything belonged to their husband.
It's not quaint or proper etiquette to erase a woman's name and personal identity; it's an incredible lack of respect.
3. Using someone's mother's maiden name as a security measure.
This is oddly an issue that didn't fully occur to me until recently, when Abe and I opened a joint account together, and the banker asked him for his mother's maiden name to put in the records. Ummm, my mother-in-law's "maiden" name is her current name! His parents were married, she just chose not to change her last name.
The concept of making one's mother's maiden name as a required piece of information assumes two things: everyone's mother is married, and every woman who's married changed her last name. Now, this may have been a reasonable enough assumption 30 years ago when my MIL was a, likely rare, exception, but it's far from unusual now!
Nowadays, I can choose to keep my name, my husband could choose to take my name, hell, we could even create a brand new name to both take. Sure, you can still give whatever answer you want to the question, but even asking the question reinforces the norm that taking your husband's last name is "just how it's done". It's cultural infrastructure that supports the continued belief in a patriarchal expectation. That's not ok.