Internet providers are used in Piwik to detect the user's countries. For example if the hostname is x.y.z.free.fr we know the user uses french internet connection.
However in many cases the reverse dns lookups return .net, .com. .org domains which don't give the country information. Piwik then guesses "USA" which is incorrect.
we should build a lookup tables of known providers -> countries
The list would simply be stored in a php file which would be fast for Tracker to lookup. This would be a new step in the country detection algorithm.
Sounds like a good idea @matt, but I have an even better idea: Use GeoIP!! (PECL or Apache for top performance)