Google says to not use Google Maps while driving - use Google Maps Navigation instead

Since launching Google Maps Navigation with the Motorola DROID back in the fall, Android users around the world have been enjoying the free turn-by-turn navigational service from Google. However, the company frowns upon using a good chunk of their Google Mobile products while operating a motor vehicle – so that means no Google Maps to aid you while driving. Apparently the Google Maps team is spreading the awareness about the dangers of distracted driving with the Oprah Winfrey Show and other organizations across the country. Conversely, Google quickly points to the exception of Google Maps Navigation which is designed for hands-free use with a car dock – but some argue that it still doesn't quite complete the true hands-free experience. Still, it's the preferred method over using strictly the Google Maps app on a handset which only provides on-screen text directions that can cause drivers to become distracted from what's in front of them.

source: Google