But the issue here is content that isn't worth much, and you pay a tiny amount for each piece. My application to yc shares more thoughts on this.
The best way to make a metered scheme hurt less is to hide the current charge, like an electric meter does, and only expose the value once per month. (the best way to decrease power consumption would probably be to expose the current charge in very visible and realtime way)
I just heard a great NPR story about a power company that is doing just this:
http://www.npr.org/templates/story/story.php?storyId=1247674...
But I suppose the point is that user pain needn't be rational.