I would consider one point about Google Analytics.
So if visitors come to your site with JS disabled, it won't execute; how accurate can that be? (I could be wrong on this one, they may track it just by the request for the "urchin")
I'm not knocking G.A. Always supplement stats with as many stats packages you can, as all of them seem to conflict a little bit. You should have a stats program offered by your hosting service, directly on the server.