Update as of nginx 1.2
As of nginx 1.2, this fix is no longer necessary as the functionality has been integrated into the core module.
This is a modified version of the nginx http_geoip_module with added support for proxies without requiring use of the ngx_http_realip_module. If you use nginx behind a proxy, the bundled version of http_geoip_module will look up the IP address of the proxy rather than the client.
This module looks first at the X-Forwarded-For header, which is traditionally set to the client IP by the proxy. If the header is found, GeoIP uses that IP address rather than the client IP address.