Google just published new AJAX API function ClientLocation for IP Geolocation.
It is cool and practical for use even without displaying Google Maps, as you can change behavior of your website according location of the visitor.
I wrote a typical example application Google IP Geolocation Map and Address which you can just copy and paste.
What IP database is Google practically using? Anybody knows? Is it their private or they are licensing one from another company?
Is the quality of IP geolocation better then free GeoLite City from MaxMind?