The details are here : http://www.nonlinear.ca/blog/index.php/2008/02/27/how-to-tune-microsoft-search-server-express-2008-etc/ 

Why Does this Matter to Microsoft Search Tuning?

Good question. It matters because Microsoft provides tools for tuning search performance that allows you to deliver superior results for each.

Addressing the Short Tail: Using Best Bets

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Addressing the Mid Tail: Leveraging Authority
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Addressing the Long-Tail: Zero-result pages and Synonyms

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