I read recently in an AdSense blog or email (sorry, can't remember exactly) that ad relevance is increased when the AS code is placed near the top of your html <body> block. In fact they, recommended that it be the first code entry in <body>.
I have always wanted search bots to see my most important topic content first, usually leading off with an <h> tag. I always thought this was best practice for search indexing.
Conversely, I have coded my AS blocks as the last item in my code, assigning it visually with absolute attribs. This decision was based on the fact that AS code is of no importance to search indexing.
Do you think I was right? Or is the AS recommendation a good one? Does it set up a trade for more ad relavancy at the cost of some search index quality? How do you code your AS blocks?