I just downloaded Blender 2.57, and when I save a .blend file to the asset folder, the console says "Blender could not convert the .blend file to FBX file." I've never had trouble importing a .blend file from Blender 2.49, but I'd never tried a file with an animation either. Is the error because of the animation or the new version of Blender?
In Unity-BlenderToFBX.py replace from line 53:
io_scene_fbx.export_fbx.save(FakeOp(), bpy.context, filepath=outfile, GLOBAL_MATRIX=mtx4_x90n, use_selection=False, #EXP_OBS_SELECTED=False, EXP_MESH=True, EXP_MESH_APPLY_MOD=True, EXP_ARMATURE=True, EXP_LAMP=False, EXP_CAMERA=False, EXP_EMPTY=True, EXP_IMAGE_COPY=False, ANIM_ENABLE=True, ANIM_OPTIMIZE=False, ANIM_OPTIMIZE_PRECISSION=6, ANIM_ACTION_ALL=True, batch_mode='OFF', #BATCH_ENABLE=False, #BATCH_GROUP=True, #BATCH_FILE_PREFIX='', BATCH_OWN_DIR=False, use_metadata=True) # I don't think HQ normals are supported in the current exporter
Blender 2.57 is not supported by Unity yet.
In Unity 3.2 they added support for Blender 2.55.1 and later., however since Blender 2.57 is the first stable version of Blender 2.5x, they apparently changed something that broke the Unity integration.
This means that you need to export the Blender files as FBX
(This thread from the forum gives the same answer: http://forum.unity3d.com/threads/85753-Blender-2.57 )
Pull up the model in blender, go to help menu and select f curve/driver version fix. Worked for me. Cheers.