You can increase the amount of history Safari maintains by running the following from a command line prompt:

         bash$ defaults write com.apple.Safari WebKitHistoryItemLimit 15000
         bash$ defaults write com.apple.Safari WebKitHistoryAgeInDaysLimit 15

in this example, Safari will throw away history items when there are more than 15000 item OR when items are more than 15 days old.

-- DarrellSchiebel - 23 Mar 2007