1)
Blender2) It\'s free software released under the GNU GPL, .Both \"free as in freedom\", and \"free as in free beer\"

3) .blend (Blender native format) its a Scene file format, but blender also native import and export for DXF, Inventor and VRML files, and througth python scripts many other 3D formats, like .3ds, cal3d, CristalSpace ( XML world files)
4) .blend. Maybe ( I hope) in the future .cal3d and CristalSpace ( XML world files)
5) between 0 and 1, closer to 0

6) maybe my opinion it;s not so valuable, because I\'m using blender mainly in a hobbyst way, i\'m not a pro, only a entusiast whit delusions about being an 3D Gaphics Artist

PD: For the blender maniacs & PlaneShift artist out there, a new project is born :
CristalBlend enjoy!
Sorry for my bad english.