just feed it a Rails production log...

~/dev/logjuicer$ rake juice:import LOG_FILE=~/tmp/production-27.log RAILS_ENV=production
(in /home/jason/dev/logjuicer)
reading: /home/jason/tmp/production-25.log
|===========================================================================================
============================================================================================
============================================================================================
============|
Parse finished in 36.94847 seconds. 6207 entries read. All log entries imported into current 
environment's database.

...and see what comes out!

screenshot 1 screenshot 2 screenshot 3
screenshot 4 screenshot 5
screenshot 6 screenshot 7

Try out a live demo:

Live demo of LogJuicer loaded with a real Rails production log

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Visit the Google Code page for LogJuicer.