Jahka has started documenting the new particle system at the Blender wiki. Its in the early stages and not everything is covered, but it is a good place to find information on the new system if you are testing one of the development builds.
Its also nice to know that documentation will be detailed and readily available for this flexible new particle system when it is released.
Check out the information at the wiki here.
A BlenderArtists thread has been started by Jahka in regards to the wiki documentation here.
And if you are a Window's user a new updated particles build is available at graphicall.