Quote Originally Posted by joysof
That's not quite true. It is used in colloquial speech fairly often. You could say: "Маш, поцелуй меня; Сань, дай закурить" instead of "Маша, поцелуй меня; Саня, дай закурить", which is formally "more grammatical".
Fair enough, but you wouldn't usually use it with anything other than a proper noun? Or would you?
Difficult to say. Мама, папа, батя, бабушка, дедушка, баба, деда, тётя, дядя, and their dimunitives -- very likely yes. Strangely enough, "сестра" will hardly have such a vocative, I do not know why. On the other hand, "сестрица" might. So there are some irregularities. The whole feature being somewhat "optional" and "sub-standard", it's not surprising.