This is obviously my own perspective, but for something as simple as sharing my knowledge and typing up a reply, I don't mind doing it and operate on the principle of all of us benefiting from the collective knowledge (e.g. I answer questions, but also ask questions and hope for a correct answer from the group)
But if the action is more concrete (e.g. I have to meet someone in person to deliver or receive art) then I would expect some sort of consideration. In fact, when I ask these types of favours from friends, I typically compensate them in some way.
Malvin