If you need the money, and I mean need the way it’s meant to be used, then all the power to you. Or, if you are able to drive significant income from it, again, I’m happy for you.
But, for the vast majority of everyone else, what is wrong with you? It’s like sticking, largely random, ads on your car.
First of all, you are worth more than that. Second of all, your readers are worth more. I’ve said it before, and I’ll say it again, if I have to use http://www.readability.com/ on your blog, you are failing. And ads, along with small font and small line-height, is what makes me hit the readability shortcut.
If the monthly charge for hosting isn’t something you can justify, then use one of the many amazing blog hosting services, including wordpress, tumblr and github.
And let’s be honest here, ads on blogs is way more common in some communities than others. What’ that all about?
Seriously, what’s wrong with you guys? Just stop it.