I think the purpose is clear - free maps, and free navigation, eventually. Bugbyte tited this fairly well as the FreeNav Project - i think it works, no?
We are facing a chicken or egg situation, we can keep discussing which data we need, or start by collecting the basic NMEA raw data and then look at that to determine what other types of data we should collect.
The expectation is that we can pool the Open Street Map data, we can also use freely available US data, which OSM used to get started, and if there are enough people actively uploading tracks, we will be able to also attract people from outside the forum to help us improve the maps.
The key is that we are setting out to do this in an open and crowd source fashion.
Step number one is proving that that we can do this project, by demonstrating that we are able to get people uploading the tracks.
Also - should we all agree on where to keep open source software? The other day someone suggested http://github.com/ instead of SorceForge. We should choose one and I can create an account. Thoughts?