I agree, this is very useful. Entering address information into separate fields is something we have, sadly, come to accept. From a user standpoint though, this makes no sense. I write my address on an envelope, and the US post office delivers it just fine. Why would I need to separate my address?

One thing to keep inmind is the Geocoding limit. If this is used on a busy website, you'll need to build in checks:

http://code.google.com/apis/maps/faq.html#geocoder_limit