With me, it depends.
I am not naturally chatty, and I don't tend to strike up conversations myself... but I will always exchange at least a "hello" with my seat neighbours, and sometimes conversations will just develop naturally.
I don't like it when people just talk to me incessantly, assuming that I want to have a conversation with them (fortunately this hasn't happened very often) - but I've had some very enjoyable in-flight conversations which, somehow, just "happened".