It's a common thing in the U.S. when you look up driving directions on Google (or Yahoo) maps, print them out prior to a trip. Personally, I use the Google Map app on my iPhone very frequently. However, finding the way around in other cities around the world, especially in the less developed regions, is a different story.
I was in Hanoi (Vietnam) about a month ago and could hardly rely on Google Maps. It provides no driving (or even walking at some locations) direction there as the map was not updated fast enough with the creation of new streets. I didn't find any alternatives there, either. The iMapsPro-Hanoi iPhone application I bought was completely useless, as its map was actually even pathetically outdated.
OpenStreetMap (OSM) is a free editable map of the whole world, much like Wikipedia for mapping. The free service allows everyone to view, edit, and use geographical data in a collaborative way from anywhere on Earth.
First created in 2004, OSM is now offering maps of cities around the world with varying levels of details and services by region, depending on the participation of the locals, which the organization tries to grab via mapping parties.
In Hanoi, the mapping party is a free educational event that teaches the attendees how to use GPS devices to collect and contribute mapping data of the city to OSM.
The detailed OpenStreetMap of Hanoi (as well as of other cities of Vietnam) is available online. The organizers of the event hope to further increase the details of the map and add more features, including driving directions.
While in places like the U.S., the existence of OSM seems rather insignificant due to the intensive coverage of online mapping services from Google, Yahoo, and Microsoft, I believe OSM is a very important alternative for other parts of the world like Vietnam.
With the fast pace of development, it's probably the only way to keep maps of the city updated--of course, with sufficient participation of local people. Hopefully next year when I get back, I won't get lost again in the city that once was my hometown.