Saying thank you is proper! It is polite. It is loving. It is cool. It is socially acceptable. It's even fashionable! The trouble is that there are a lot of unfashionable people around.
Most of them probably don't know any better. Their education has been neglected. They've not been taught at all, or whatever their mamas or grandmas (or dads or grandpas) drilled into them they've forgotten. It's too bad. I don't *think* I'm a terrifically conceited or selfish person, but when I do something for someone and am not thanked, I wonder if what I did was worthwhile. Perhaps the person didn't like what I did or gave. I genuinely wonder if it would be better not to do anything in the future.
When you receive a gift in person, you *say* thank you. But if it's a significant gift - to the giver and/or to you - it's also a good idea to write a note or at least e-mail. You do the same thing if someone has done something for you - for instance, letting you stay at his/her house or letting you borrow a car for a few days when yours is in the shop. (If you write a snail mail note, you use little note cards, so that you don't have to write a whole lot - just a sentence or two naming the gift or the service and telling your appreciation.)
Some people telephone their thanks; I don't happen to be one of them, but it seems to be all right for some occasions. Often, when my children or grandchildren visit, they may e-mail their thanks, and that's fine with me. I don't know about texting, but maybe it's OK for someone who can translate it.
It's not a matter of someone's keeping or not keeping a thank-you someone sends (thank-you notes do not have to be responded to with thank-you notes!); it's a matter of caring enough to *say* thank you in some way to the person.
If you are going to err, err on the side of too much thanks rather than not enough.
When I say "you," of course, I'm not talking about YOU. You know all this! You can't change what other people do, but continue to do the right thing - and teach it to your children - even if you (and they) feel like a nerd.
End of lecture! Sorry. I'm off the soap box.