Google Maps already has some offline capabilities, but the company will soon release a version for iOS with full offline support. Right now, using Google Maps offline gives users the ability to see areas on a map but that's about it. The upcoming version will bring full navigation and business information lookup without an Internet connection.
This of course means that you need to do some prep work in advance of going to an area where you may not have internet service. You'll need to download an area for offline use, but then you can get directions, view business hours, and peruse ratings without having to touch your cellular data plan.
Of course, active features such as traffic alerts won't be available when offline, but this will be great for those situations when you know you'll either be in an area with a really bad cellular connection or overseas without a data plan. The offline mode rolled out on Android today and will be coming soon to iOS.