Vkontakte is populated with undereducated and illiterate adolescents - obviously a bad medium for learning - full of spam. There's nothing that can be learned there.
There are nicer ways to learn languages.

Nearly everyone in Russia has an account there (myself is not an exception) - this formally makes it one of the biggest social networks (even though they compete with the odnoklassniki). Merely a fact that they have many accounts does not automatically mean all of these accounts are active and frequently used. Once the initial boom of popularity had ceased I doublt any grownup stayed there for long. It's been months since I visited my account for the last time. Now the majority of its population are teenagers.