I think that most traffic comes from people trying to answer their questions when doing a general search on the web. Since some of the best hubbers on here answer those It would be my guess that promotional ideas are not the best way to go. If your shopping for something your probably going to go to amazon or something like that anyhow.
Adsense is supposed to suggest things they may want to buy from our pages, and to be honest people only seek those ads about 50 percent of the time.
Playing devils advocate: What about the hubbers promoting non profit sites? Do you all think that is wrong? Should it matter if they make money or not? Just curious.