Does anyone have statistics on the percentage of click throughs based on the positions in the SERPs?

i.e. If there are 1000 searches on a term, what would be a good solid average percentage to estimate the amount of traffic if you were ranked in a given position.

I know factors such as title and text used in description effect it, I'm just looking for a ball park.

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San Diego Web Designs - One man operation (with one woman doing QA)
Firms I've done or do work for: MEA Digital, SEO Inc., eTraffic Jams, San Diego Media, WebAdvantage, Online Guru
http://www.poopegifts.com - Mail someone poop, anonymously. The perfect gift for Hansel Mosh (Hansel?? Are you kidding me? No wonder he's so bitter)

__________________
San Diego Web Designs - One man operation (with one woman doing QA)
Firms I've done or do work for: MEA Digital, SEO Inc., eTraffic Jams, San Diego Media, WebAdvantage, Online Guru
http://www.poopegifts.com - Mail someone poop, anonymously. The perfect gift for Hansel Mosh (Hansel?? Are you kidding me? No wonder he's so bitter)