For quite a while I've had Google Adsense ads on my websites. I can't put them here, because I discuss the ads on this website and I don't want to violate the Google TOS. I must say that I am very happy with the ads.
Google won't let me publish the statistics, but I can say that for every 1000 views of my web pages I make anywhere from $1 (sometimes less) to $10 or more depending on the website and time of year. Musical Instruments do better than SpecFic and Aviation does better than cats.
If you don't have Adsense on you web pages, you are crazy. It is free money. Ads are innocuous. You can put them in an out of the way corner, although they work best at the top of the page or in <div style="float: left;"> box.
Lately I have been experimenting with paying for clicks using the converse of Adsense; Google Adwords. Starting at 5 cents, you can send clicks to your web pages. I am using this for FreeNameAStar.com and the harmonica sites. The trick is that I pay the minimum for a click and these sites usually get more than that for each click on the ad. There are people who tend to click ads. When they click on your site, they click out again on a new ad. This is called "Click Arbitrage". It is, so far, working for me. I am paying about $3 a day for clicks and my click revenue goes up a few dollars a day. In addition, my Free-Name-A-Star site is getting 3 or 4 paid registrations a day so I am showing a nice profit from the advertising. This is three times what I got without the advertising.
I would recommend, then, that anyone who wants to increase the circulation of a website, sign up for Gooogle Adwords. Set yourself a budget of $20 a month, make a nice text ad, and see if 400 new users will help your site. My experience was that a good chunk of the new users are "sticky", that is they come back for more. I used this on AudioCD.com when I was pushing that site. I would get 10 or so new clicks a day, but that steamrolled as the new users came back and became regulars. I was getting 100 unique users per day and after a month or two of Adwords I was getting 500 unique users per day.
So here's what you do. If you sell books (J!) make the sales page with two or three google adsense ads on it. Put them in floating divs on the side and a banner at top. You can't have more than three ads. Then go to Adwords and make a cool seductive text ad indicating how sexy your books are that points to your book sale page. Set yourself a modest budget, just to test. What I think you you will see is your book sales going up and those people who don't want a book will click on the ads and more than pay for your inbound clicks. You'll get some people who bookmark the page and come back over and over again. If it doesn't work after a month or two, you can cancel.
Two things - 1. never click on the ads on your site. 2. never talk about your ads on a website that uses the ads. Google is watching you. It is too good a deal to mess up.