Google's recent update for the Maps app introduced a variety of new features and improvements. One of those is the ability to save map data for offline access.
If you use Google Maps on a Wi-Fi only iPad, or if you'll be traveling somewhere where cellular data is spotty, knowing how to enable offline caching of map data is pretty important. CNet explained the trick recently.
First, you'll need to zoom in a bit; you can't cache a widely-zoomed-out map view. Then, when you're at the spot you'd like to cache, type
OK maps into the search box, and then tap Search.
When you do that, a Google Maps icon will appear briefly, followed by a message indicating that your map data was saved. Now, even when you're offline, if you navigate to your cached areas, the map data will appear.
Mac OS X Hints