If you are operating a search engine marketing campaign in AdWords, Overture, or other service, consider targeting the 2nd and lower positions for your advertisements. The top position is often bid up unnecessarily by competitors, and it also attracts a much higher percentage or poorer quality clicks than do lower ad slots. The latter occurs when searchers do not distinguish well between paid and free search engine results, when ads are placed on broadly applicable terms, and/or when the ads do not sufficiently inform users in ways that may prequalify them before clicking.

A more detailed discussion can be found here: http://www.web1marketing.com/resources/articles/dont-bid-for-top-placement.htm