When parsing an address with an apartment number, you receive a "Subpremise" attribute. This attribute is typically mapped to an "Address Line 2".
For example: https://maps.googleapis.com/maps/api/geocode/json?address=2123%20W%20Mineral%20Ave%20Apt%2061,%20Littleton,%20CO%2080120
It would be nice to have this added as the subpremise on the Address object.