Just this past Monday, my company, Stone Temple Consulting published the initial results from a competitive comparison of 7 different analytics packages running across 4 different sites. Philipp Lenssen asked me to post about the report in the forum here. You can see the report here:

   http://www.stonetemple.com/articles/analytics-report-may-2007.shtml

In it, we ran the packages simultaneously across the 4 sites (none had all 7 packages, but some had as many as 6). The report then publishes detailed numbers showing how the various packages did for a wide variety of data.

It was interesting to see how the data varied from parameter. Google Analytics and Clicktracks tended to report high, and HBX Analytics tended to report low, but this was not always the case.

We also ran a test to see how the non-acceptance / deletion of third party cookies differs from the non-acceptance / deletion of first party cookies. This test showed a difference of 13%.

I will check back here to see if there are any questions that I can try to answer.