Going back to the Nikon fisheyes - it's interesting to see that they thought they would be useful for 'general photography' as well as specialist applications (just how many 'general' shots can you take with a 6mm
)
That 13mm in the super-wide lens group looks an impressive piece of kit - anyone ever see one of those? (16 elements in 12 groups, 118 degree field-of-view, 1200gms).