Can you really make money out of blogs?

Well I am starting my trawl for how people make money out of their blogs. My first port of call was the Adsense option on blogger.com, the second port of call was of course Amazon, where I signed up as an Associate. Took a look around the associate information. The main idea was to write the occasional book review and to leave a link to the book in the blog. You get 15% of the list value credited to your account if someone follows the link and buys the book. There's also something called a "self-optimising link". This is a kind of banner ad which adapts itself to the content of your web site. So as a starters I copied the html provided by Amazon into the bottom of the blog template, just above the footer, ... et voila, nice little Amazon ads appear at the bottom of my blog page. Nice, but retirement plans still on hold.