"The Conversions by keyword position report is really useful. It confirms what I guess most people have suspected all along, i.e. if you want great conversion, you want the t1 position top across the page. If t1 is not available, you want position 1, i.e. top in the right hand column. These positions outshine everything else in terms of conversions. At least for the 20+ top keywords that I just checked."
Be careful assuming that a general statement like this applies to you. I believe it is very important for advertisers to know that this comment does NOT hold true for most advertisers. I would be very interested to know what the person who posted that is advertising.
The T-1 position will definitely get the most traffic but much of that traffic will come from people who just clicked on the first thing on the page and did not read the ad.
I see much better conversion percentages for other positions and a huge difference in ROI. I intentionally keep most advertisers ads out of the top two positions but I have had a lot of ads in the past that end up in T-1 through T-3 and honestly those positions generate the largest percentage of traffic and poor conversions in general.