Using the latest Blender build, the models I import into Unity 3.4 sometimes will not show up at runtime. It will appear properly scaled in the Scene window, but not at runtime. It just “poof” disappears. I have checked the plane mesh it sits on (Unity Terrain GameObject) to be certain it does not fall through and everything is ok in that area. This is horrible, I have just figured out how to do the colliders and such and now this. Arg! What could I be doing wrong or what could be amiss?
Move the object to 0,0,0 in the scene, and see if it stays there… if so its an issue with the imported animations (usually “Default Take”, and can usually be fixed by removing/disabling the animation component)
If its not that, maybe add a comment to your original post with version info and export/import procedures you are using