I'm interested in utilizing urchin.
What are some advantages of self hosted analytics software like urchin over Google analytics?
This page http://www.google.com/urchin/features.html has a comparison table. The features that it has that Analytics doesn't are:
It's not cheap though: US$9995
Each have their own strengths and weaknesses. You need to decide which one's strengths would serve you best and while it's weaknesses do not hurt your ability get usable data.
There's more to it then this so you should definitely do more research on your own. The information is definitely out there. But this should give you an idea of how to compare the two to figure out which one best suits your needs.