Over the years I've tried many web log analysis tools both commercial and free and in my opinion the best thing available now is the free Google Analytics service. Microsoft is coming out with a similar poduct called Project Gatineau but it is currently invitation only.
As of version 2.2.6.8, mojoPortal now has advanced integration with Google Analytics.
Other tools do log analysis whereas google tracks actual pages as they are viewed. I also download my log files and and process them with a free tool, awstats, but I find it exaggerates traffic due to all the bot and crawler traffic.
Todd Lewis has also done some work using Webalizer. He has a technique for parsing the logs from a multi site mojoportal installation so you can see traffic reports of the individual sites. He started some documentation on this here: http://www.mojoportal.com/multisiteweblogtricks.aspx
Tip: You don't have to wait till the next day to see todays traffic in google analytics. Just set the begin date and end date of the the report to the current date.
Last Modified 2008-08-16