GeoRiot is a service that copes with the complexities of mapping IP addresses (and other clues) to a geographic location. I first heard their name while talking about affiliate marketing. They've since moved into the industry more fully offering a free (pay in clicks) geolocation for Amazon affiliation.
The solution works by redirecting your Amazon links to Amazon US, UK or JP but claiming 15% of those clicks as their own - so they can get the affiliate commission. They've a similar deal for iTunes.
GeoRiot have been doing a bit of social media research; using Klout, PeerIndex and raw Twitter stats to work out who identifies themselves as affiliate marketers and who has reach. The exercise tells me affiliates are busy making money and not really promoting themselves as I've managed to rank 7 out of 25 in a global list. I'm the top European marketing mind for affiliates. Well. According to this flattering research!
You can read up on the research and get contact information for everyone listed here over at GeoRiot.