Maybe there is another alternative.
OpenWebAnalytics is also a free software.
It runs like Piwik on your own server.
But it needs a lot of cpu-ressources!
During our first test-setup, the cpu load (2 cores) was always over 90%.
Now with 4 cores it runs well.
We are using two setups to track different online-shops and a typo3 instance.
The typo3 instance has around 60.000 unique visitors per day (this setup had this amazing cpu load).
What I really love is the tracker of mouse oriented events (DomStream).
A great chance to optimize your landingpages.
You can get more information on the subdomains wiki and demo on OpenWebAnalytics.
But be carefull, it is still under developement.
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I'm sorry, but I couldn't insert the direct links to page, wiki, and demo.