The trend to open data is accelerating. April 1, 2010 the Ordnance Survey opened much of its data and now ESRI is helping organizations make their data open and freely available to the public.
ESRI has announced that any organization subscribing to ArcGIS Online can enable open data over the web. ArcGIS Open Data is a public beta for open sharing of data from ArcGIS Online.
Data providers can specify open data groups that are open to the community to be shared, downloaded, and reused in other open data sites and applications. I assume the licensing is determined by each organization.
Data consumers can access open data sites to download data in common formats such as KML, comma-delimited (CSV), Shapefile, GeoJSON and via web services.