Q:

Complimentary close «С приветом» still existent nowadays?

I learned during my classes that I can close an informal letter to my familiy or friends with С приветом, твои сын for example. 
As I showed a couple days ago my homework to a real russian woman she laughts and said this means something like to have bats in the belfry and I should better use пока or до свидания.
So what is this all about here in your opinion? I putted this into the Google Image search and there came up some stuff which points into the direction my Russian padruga said.

A:

Well, there's a "common-language" meaning of "с приветом" (crazy, nuts). So it's not much popular today as formal closing. Nevertheless it's still OK. But if the person not knowing this (a foreigner) writes so, some people could think it funny.

A:

Well, a female friend is still podruga, not padruga, and 'your' here would be tvoy (masc.sg.), not tvoi (pl.); the language did not change that quick in the part of its orthography. As for the complementary close, it has a double meaning and semantically is actually closer in the modern Russian to 'be crazy', but that mostly works in phrases like Они с приветом / Он с приветом.
This complementary close stands for any other one of the same structure, like
С уважением
С уважением к Вам
С наилучшими пожеланиями
С поздравлениями
С восхищением (if you want to flatter a bit when writing a romantic letter)
С пожеланиями успехов / удачи / всего наилучшего (any Genitive attribute would do).
The priviet also can be used, but then it would be better specified as a form of greeting, e.g.
С дружеским приветом 
С английским приветом
С американским приветом
However, such a complementary close would be regarded by most native speakers as a manifestation of utter / absolute trust, which would really be a little bit strange for them.
The calques from English also would do, e.g.
Всего хорошего
Искренне Ваш / Искренне Ваша
С наилучшими пожеланиями

