Well, the database was downloaded from this site
http://ip-to-country.directi.com/
These dudes claim that their free database is IRIN's database with several small enhancements
As you can see Rasmus (the PHP creator) is using the same database on PHP.net, so I think that's enough to say it's a good database.
As you can see, on the MySQL tests, The algorythm to track countries used by CjOverkill can track about 10000 country queries in 12 seconds on a P4 1.7Ghz