Also very relevant:

http://openstreetmap.org/ (and http://wiki.openstreetmap.org/)

Maybe someone would like to write a site that allows for updating postcodes in any country? And, ofcourse, provide queries via an api.

There are various different query APIs available. Google maintains a useful list:

  http://groups.google.com/group/Google-Maps-API/web/resources-non-google-geocoders

One of the major problems is that the use of the data returned by many of these services is restricted. There are a couple of entirely free solutions. For example, I put together Fetegeo http://fetegeo.org/ to show that it is possible to have fairly decent search facilities with solely free data (though the currently available data sources all have various limitations). I keep hoping that someone will take Fetegeo and plug-in data sources like Openstreetmap.

Google provide an API for the UK that basically gives you a lot of the 'clever' stuff that Maps provides in terms of finding an address which can be quite useful. Not sure if this is available in other countries...