I am using Blender 2.49a (2.492) and Unity 3.1.0f4. Unity seems to be importing the files. It does not give an error message, but when I drag the imported asset into a scene to instantiate it no mesh shows up. The created GameObject does not have a mesh renderer component. When I import the same models indirectly by exporting them to .obj from Blender first, the asset shows up in the project with an arrow to the left of it, like a folder, or a prefab which contains an object that has children. When I try to import directly from a .blend file, there is no such arrow. See the image below.

The top asset is the .obj file. The bottom is the .blend file.