I take issue with G's recommendation for skyscraper ads (not sure what "rectangle" ad is being referred to above but I find skyscrapers to be one of the most troublesome ad formats to work with in general). I often see them regularly out-performed by smaller horizontal units and units loaded after and before them in the html. Their text formatting has also been an issue of contention for me (ugly not that others aren't as well). I'm generally convinced that the horizontal leaderboard is still king but you'd be amazed at what simple link units can achieve or even mobile sized ads placed appropriately. As for progression in page flow and all these other recommendations G makes, I'd love to see them put their stats where their mouth is because the majority of recommendations are just hogwash (designed to benefit advertises more than publishers) and the best advice I've heard from anyone is to just build your site for a pleasant user experience first and foremost. That's really the only Google recommendation I follow regarding ad placement.