Damit ihr nicht in rechtlichen Schwierigkeiten kommt müsst ihr bei Google Maps aufpassen:

Code:
(b) No Pre-Fetching, Caching, or Storage of Content. You must not pre-fetch, cache, or store any Content, except that you may store: 
(i) limited amounts of Content for the purpose of improving the performance 
of your Maps API Implementation if you do so temporarily (and in no event 
for more than 30 calendar days), securely, and in a manner that does not 
permit use of the Content outside of the Service; and (ii) any content identifier 
or key that the Maps APIs Documentation specifically permits you to store.
 For example, you must not use the Content to create an independent database 
of "places" or other local listings information.
Da verstößt man sehr schnell gegen deren Nutzungsbedingungen.