I make a chunk of change each month from running Google ads on this and my other Web properties. How much? Let's say enough that Google sends me a cheque each month.
I'm also participating in Google Print. That's where publishers can have their books hosted by Google's search engine. The usual things apply: when people search for passages in books, ads are displayed and there are links to buying the whole book. Except that they have to use Google Print for seaching.
After ten months of my books being live on Google Print (after taking a half-year to get live), I've made $8.12 -- not enough yet to get paid.
After reading an anlysis by Bill Trancer, I now understand. He found that Google Print gets 0.25% of all Google traffic. Divide my $8 by 0.0025 (and multiply by .8) and I'd've made $2,600 -- if Google Print were linked to Google Search.
But it's not. I've complained to Google, and Google has replied, in its stilted "official" prose, that they're working on it.