First of all I would like to congratulate you for this great project and site.
I've been using the postalCodeSearch web service for translating postal codes into lat long info. The service works fine but it returns the same latlong position for different postal codes. More specifically, I'm trying to translate postal codes for spanish cities. For example, postal codes from 28001 to 28030 (postal codes from Madrid) all of them are referred to the same position (40.4/-3.683) and the same thing happends with other postal codes in other spanish cities.
I would like to know if it's common limitation or it's a problem due to lack of position information that will be improved in a future.
I think we should be able to improve postal codes shortly.
You can help us find free data sets. The Ministerio de fomento for example has a lot of interesting data : http://www.idee.es
I have already asked twice whether we are allowed to use some of the IDEE (Infraestructura de Datos Espaciales de España) data for geonames. So far I have not yet received an answer. Maybe you have more luck?