I was reminded of this today because the only ads for HelpSpot I currently run are on the blog of the 9rules network founder Paul Scrivens. The ads were doing OK, but recently he changed the layout, moving the ads off the side and towards the top. Since doing this click through has been much better! Something to look out for if you're buying ads.

Here's a sample of his new layout:
http://9rules.com/whitespace/ (you may need to refresh a few times to see the HelpSpot ad)

Thanks Paul!