It's strange that Wikipedia seems to stand as an anomaly - a isolated counter-example to almost every other public forum on the internet where discussion seem to all inevitably descend into a discussion on Hitler. Somehow the creators of Wikipedia have put into place a system which appears, at least from the outside, to avoid hierarchy, free from centralised control of the information it creates, while still remaining, for the most part, accurate, relevant and reliable. It is precisely the headless nature of this monster that has sterner governments nervous. But all this is old news.
to the individual animal's pens
If there is anything we've learnt from Wikipedia is that there is a certain cross-section of society which are excruciatingly relentless when it comes to the accuracy of information. In a psychological study of Wikipedians found that they don't fare well in the five traits openness, neuroticism, conscientiousness, extroversion and agreeableness. In other words they are a bunch of spiky personalities that come together to argue about the minutiae of obscure historical subjects when they're not getting bogged down in a neverending string of definitions and counter-definitions. Not my idea of a good time though perhaps necessary to get things right. Yet, if there is any metric by which the quality of a map can be evaluated it is its accuracy. Furthermore, it would seem that there would be far less room for debate when plotting maps than regarding almost any historical subject - ie either there is a train station at so-and-so-a-place or there ain't - it's that simple. Yet if you consider the ways in which contributors can get involved includes correcting errors you can be sure that these spiky personalities are going to find something to argue about.
What OpenStreetMap is able to harness that Wikipedia cannot is that almost everyone is an expert on something relevant to the project, which is to say that almost everyone is a local to somewhere. Locals are going to know much more about their locale than someone else and allowing OpenStreetMap to be a composite picture for all local pictures is something that has not been attempted before.
OpenStreetMap only being concerned with mapping and not the control of information also impacts accuracy. Consider when cartographers used to insert fictitious entries into maps to prove any cases of copying - the A-Z map of Bristol had the non-existent street "Lye Cl." for instance. No such controls will be in OpenStreetMaps with a legion of hair-splitting contributors to correct an errors, intentional or otherwise. Furthermore, as the corollary of a lack of information control is accessibility, each map is open for use to whoever for whatever. The addition of different layers to maps, for example, allows someone to superimpose any Geostatistical information over the top. This includes crime statistics or demographics to be overlaid to see what is happening where. In addition to this there are different maps for different purposes - there are bicycle maps, marine maps already for OpenStreetMaps.
The real power of OpenStreetMap is in its use not its generation. I am in the middle of planning a motorcycle trip around the Caucasus and actually finding a way to navigate around there was extremely difficult. In terms of commercially available road maps the best I could do was a German made fold-out number, in the not-so-great size of 1:650,000 which was already a year old when it was delivered. Sure Google maps is great on your home PC but to get it onto a phone requires pre-caching and awkward third party software if you don't want to be slugged with a huge data usage charge on an Armenian network, plus who knows what local controls they have in place when you're there. Another option is to buy proprietary maps for your GPS - these come out once a year so are not going to be as up-to-date, plus if you are travelling to many different regions it's going to get quite expensive. For all my entire route I was looking at paying at least $500 for the maps alone. Instead I was able to go to http://garmin.openstreetmap.nl/, highlight the map tiles that were relevant to my trip, submit my email address. Moment's later I received an email with links to the map that could be loaded directly onto my GPS. All free. Admittedly I had some issues with the routing but I'm quite sure that was due to the GPSs mapping engine - not OpenStreetMap.
Governments have historically been extremely nervous about maps as they have been with other information. Imagine,as I have, that you were arrested as a spy as you were plotting a road to submit to OpenStreetMaps in some backwater country under a despotic regime. Your first reaction would be that that is a ridiculous concept. But when you consider that you are recording data and uploading it to the irrepressible internet cloud you might see things differently. In other words, maps are a fundamental tool of control provided the information they contain is controlled too. OpenStreetMaps is the first mapping database to be as yet unanswerable to any one person or regime. As the completeness of its data set becomes less and less about the development of uncharted parts of the world and more about how easy it is to get information out of certain places, OpenStreetMap will have unintentionally provided a political map where detail is equated with freedom, and lack of detail with repression, showing exactly where all the dragons be.