wow, noone has explained the nautilus(sp?) shell design. I remember reading about it a while back, that design was actually made to completely cancel the wave coming out of the back of the speaker..as reference, think about ported designs that make use of the back wave by use of a tuned port. That "cabinet" does away with it all together. Something about clarity of sound.
I need to re-research it, but that's the jist of it...beautiful design.
As for odd shaped cabinets, i remember seeing some cabs made out of bass drums, actually stackable as well, cant remember the company name for the life of me though.
-James