A word of warning!
If you use the contacts database in Sitecore 8 you might run into some serious issues when upgrading to Sitecore 8.1 Update 1.
It seems that the datatype of the GeoIp has changed length from 4 to 16 characters. The 8.1 code does not handle the backward compatibility at all :(
I started a ticket with Sitecore Helpdesk on this issue, and was asked to run this little tool on the MongoDB Analytics database.
That seemed to solve the problems.
Thanks to Alexander Vasilenko and Ivan Sheyenko from Sitecore Helpdesk for helping solve this issue.