It started four years ago in the UK as a project to create a free and editable world map. What began as a few geogeeks wandering the streets with their GPS’s has turned into a global movement with over 75,000 registered contributors.
check out the animated gif on how it developed over the past 2 years here
I find it impressive how committed some people are:
Most impressive has been the takeup in Germany: 300 volunteers mapped 99.8% of Hamburg (German), and there is now a German-language OpenStreetMap book. (I am sure it will be 100% soon – they are german 🙂 )
There are other things too – like a OpenCycleMap which takes the base OSM data and renders it slightly differently, giving emphasis to features relevant to cyclists.
As a result in many parts of the developing world OSM is now the most comprehensive online mapping available, for example see this comparison of online maps of Baghdad.
There are more examples on how OSM is better than the others:
I find it very interesting and I am glad there are so many people out there that spend their free time making our lifes easier.