blogger give away free blog hosting.
they are also pretty fine about letting you host ads on your blog.
Didn't know that!
But as root pointed out, still not something you're going to earn any money on, realistically.
FWIW, I sort of ventured down this road once in the past, around 5-6 years ago - a friend and I started a technology site and wrote about various topics, some of the content was great, some was controversial (always good for generating views) and some was a bit mediocre. It was more of an experiment rather than anything we hoped to make money off. We aggressively promoted it, got on the front page of digg twice (back when digg was huge) and managed to get it up to, at its peak, just under a thousand hits a day. We spent a lot of time carefully using keywords to target appropriate adverts to our audience, and followed several guides for putting them in prominent pages where people would be likely to click on them.
In the couple of months we were doing this, we raised something like just under £10 in advertising revenue - and that was a lot of work.