Google has primary used two sources of data for their Google Maps product. Google announced in a Google Groups thread, that they are going to be sticking with just one source for the foreseeable future. That source is Tele Atlas.
Maps Guide Adam explained that Tele Atlas powered Google Maps API and Google Maps for Mobile fully and will now power Google Maps fully. Adam explains that you should see many improvements, but there may be some issues with some locations.
While most of the map will look the same, and in many areas it will improve, there may also be some cases where the data may not be optimal.
If you find issues, Google recommends two things to help improve the map tool:
Forum discussion at Google Groups.