I stuck some Google ads on the blog when I first started it. Not because I expect to make any money from it, but I use Google ads on one of the community pages I run to try to help cover hostings costs. (The site, Två Katter, is currently down while I switch over to a new content management system that's more secure than PHP Nuke.) The ads are selected based on the content that Google finds on the pages. I've even found it useful -- it was the ads that led me to using QuadLock for the concrete forms.
But I was amused the other day to see the latest set of ads: Prevent Overheating. Buy Temperatute Sensors. Recycled Antifreeze. All based on my early blog entry about the problems with the U-Haul truck. So at least Google is reading my blog :-)