Strangely enough, nobody is buying the 160x600 size on my sites. Don't understand why, perhaps not many advertisers have that size in stock and don't want to create one for their campaigns, but 125x125, 300x250 and 728x90 are selling fine, it's just that 160x600, weird since I think it is a good format and when you count the total number of pixels, for screen estate it is the biggest: 160x600 = 96,000 300x250 = 75,000 728x90 = 65,520 125x125 = 15,625 But it is part of the recommended sizes.. The ad location is in the sidebar "of course" since it fits mostly only there, but I have people buy ads of other sizes which are lower down the page fold.. I think this format is good when the ad is made for being read vertically to prompt curiosity of the viewer.