I didn't find anything like this with a quick search, so here's an idea that may have been brought up before.
What would be involved in getting a new widget (or set of widgets) that would list music I'm listening to, books I'm reading, and/or movies I'm watching? TypePad has a similar feature, I believe, that pulls from Amazon. If a click on the link leads to a sale, then WordPress could get the kickback through Amazon's program (which then gives WordPress some potential revenue from the blogs that make use of the widgets).
This seems to give some of the benefit of placing ads on the blogs to support the overall operations, but is entirely opt-in and the items are user controlled. On the user side, we get to display favorite music albums, books, movies, and whatnot in our sidebar.