Google has added an experimental feature called ‘Download map area’ to Google Maps for Android. It allows customers to save a 10-mile radius of any chosen place before arriving there, enabling them to reduce data costs or prepare for locations without mobile connectivity.
It’s necessary to have the latest version of Google Maps and to activate the the option from within the ‘Labs’ menu.
A WiFi or 3G data connection is still needed to see a satellite/3D view or to search for places and directions. Cached maps are stored for 30 days.
[Google Mobile blog]