AS long as it adds value to the site, then I think that the advertising works. I have some small AdSense ads on my site, and they usually target the ads pretty well. And if something pops up that I don't approve of, then I can flag it as one that I do not want to appear on my site.
I also use the affiliate programs to target specific books that I think add value for my readers. It is sort of a "for deeper study in this area" reference.
I don't make a ton of money off of any of it. However, after about a year I have about $60.00 built up in my AdSense account (it pays out at $100), and it is progressively growing faster each month. And I have "sold" about $1,500 worth of books which have resulted in about $150 in commissions for me.
The book site references I think add the best value. I have seen readers at my site follow certain posts and then order 10-15 copies of certain books (probably for a small group study). But if I am "selling" over $100 worth of books every month, then that tells me that there is enough interest and value to keep it there.