Google Maps doesn't have street-level maps or information about local businesses for many countries. To make the service more useful in countries like Cyprus, Vietnam, Iceland, Pakistan and the Caribbean islands, Google launched Map Maker, a way to add or edit features, such as roads, businesses, parks, schools, and place them on a map. After submitting the information, it will be available at the Map Maker sites for other users to edit it and you could expect to see it live in Google Maps when Google decides there's enough information.
Google recommends to use the hybrid view to locate places precisely and to zoom in to a range of 50m to 1km. You can add businesses using placemarks, mark roads with the line tool and add parks using polygons. This wiki offers more information about locating features and tutorials for all the tools that can be used to improve the maps. "This product is a labor of love by many engineers based in Bangalore who have a desire to see the world mapped," explains Google.
Another collaborative mapping service is OpenStreetMap, that licenses all the data as Creative Commons Share-Alike. The project's motivation is to create a "a free dataset which will enable programmers, social activists, cartographers and the like to fulfill their plans without being limited either by Google's API or by their Terms of Service. The data used in Google Maps is sourced from NAVTEQ and Tele Atlas, two big mapping companies. They, in turn, have obtained some of this data from national mapping agencies (such as the Ordnance Survey). Since they've made multi-million pound investments in gathering this data, these organizations are understandably protective of their copyright."
It would be interesting to see if Google decides to change the licensing terms for the data obtained from users. In the past months, Google started to allow users to edit inaccurate addresses, to add places and to collaborate on maps.