Crowdsourcing changes the paradigm by having volunteers contributing their time, and having access to free data (without complex licensing constraints) completely changes the economics of developing geospatial applications. Obviously the first reaction of most traditional geospatial people is to ask whether you can get good enough data quality using this approach. Dr Muki Haklay presented a very thorough and rigorous analysis of the quality of OpenStreetMap data against Ordnance Survey data in the UK, and his conclusion was "OpenStreetMap quality is beyond good enough, it is a product that can be used for a wide range of activities" (not in general - today - for very large scale mapping, but for small or medium scale mapping - the type of applications that today might use today data from Google or Microsoft, NAVTEQ or Tele Atlas).
The conference itself had a tremendous buzz about it, with 250 people from thirty-something countries (I think), and great enthusiasm and excitement from everyone participating. The presentations were a great mixture of people talking about really cool and innovative technical things, and heart-warming and moving stories about people creating maps from all parts of the world - in many parts of the developing world, OpenStreetMap is way ahead of any other data source.
Anyway, I'm off to be a tourist in Amsterdam for the day, I will write more in due course. If you are attending the ESRI user conference this week I really recommend you seek out the OpenStreetMap booth to find out more about what they are up to. And thanks to everyone who attended State of the Map for making it such a fun and inspiring event!