Not very active on this forum, but most PMs I send are about someone's avatar or an interesting post. Sometimes I send weird shit to people, because it's the kind of interaction I like receiving unexpectedly. Must strike me as fitting for some sort of context, though. I don't have very many PM conversations, because I do not often have more to say after one or two have been exhanged.
I respond to just about any PM I get, barring spam or things from people I don't like.