I've been using it for about 9 years. If all you need is country resolution, it seems pretty much spot on, and very useful.
I haven't seen anything that is all that accurate beyond that. Most geo location (for the UK anyway), pegs people at the ISPs head quarters, rather than their actual location. Which isn't really very useful.
I'd like to know the souce of the data and how it compares to other databases. It might be good for a prototype, but there's no telling the real quality of the data.
Be nice to have a better idea of why this is more accurate than say MaxMind GeoIP, how much more accurate it is, where the data comes from etc.