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e.g. do you have a general idea of how often an US-based ISP like AOL will ultimately pull down a page from a UK website despite the resident actually being located in a different country?
The per-country reliability is very precise. Per state/region is lower and per-city might be questionable for small cities, but for big cities it might be very precise.
The only problem I've had has been with the latitude and longitude provided by IP2Location. As an example, the database precisely locates me in Miami, FL. The map coordinates, when plugged into Google Maps, puts my location about a hundred miles east of Miami in the Atlantic Ocean. It does this with some other east coat cities too in both the Atlantic and Pacific. Most of the time though it's quite accurate.