You might enjoy reading Sheldon Brown's Revisionist Theroy of Bicycle Frame Size.
http://www.sheldonbrown.com/frame-sizing.html
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A conclusion is the place where you got tired of thinking. - S. Wright
Favorite rides in the stable: Indy Fab CJ Ti - Colnago MXL - S-Works Roubaix - Habanero Team Issue - Jamis Eclipse carbon/831