In my experience, auto ads work very well with the default xf2 theme. But can get messed up on third party themes like UI.X2 which is what I am using. But the entire implementation is pretty amazing especially on mobile devices. Google gets the color theme and layouts very well. Great product for people who do not want to insert ad codes manually.
it does experiment a lot with time and eventually finds a nice balance.
also the ads are not placed in all page loads for me. google seems to be doing a lot of machine learning for this particular product. it keeps on changing on a regular basis.
sometimes they just end up breaking the layout of the page when an ad is placed between wrong divs.
with wordpress, they are pretty amazing. forum layouts are a lot more complicated.
Perhaps the biggest issue is the ads are placed on many pages that have few visits, this results in aggravating the member who will end up using an adblock. I think it's best to place ads minimally in specific locations.