Google Analytics is Under-Reporting, or is it?

[clickdepth]

I've been seeing several posts ripping Google Analytics for under reporting data when the data is compared to Urchin / log file analysis. Based on my findings I'm seeing that Urchin maybe the problem and not Google Analytics.

http://www.imulus.com/blog/index.php/2007/01/13/google-analytics-is-under-reporting-or-is-it/

Has anyone else researched this topic?

[Rank3d]

There are some inconsistencies with mine too. I use Google analytics and Webtrends and there is a very huge difference with the number of visits, visitors, referrals, etc. For my weekly report, below is the result of my visit counts:

Google Analytics: 34,000+
Webtrends: 150,000+

Same with my search engine referrals. As you can see, there's a very huge difference.