You are right, the ads look absolutely shit - I could perhaps go with Buysellads when traffic picks up.

Interesting idea - I'm a huge admirer of things that follow that model - Michael Hartl's Rails Tutorial and Avdi Grimm's Object's On Rails.

I am hoping that people fixing cars are more transactional (read likely to click an ad) than people looking for coding tutorials. I might leave it as ads for six months and then try six months of freemium access and compare the two.