Assuming Ultra-D works as well as some here have described, one negative about it, unless I'm mistaken, is that it sounds like it would not be applicable to projector technology. It works only with direct-view displays, so immersion, like those of us with large wide screens are so fond of...
If this technology helps resurrect 3D in the US, then I'm all for it. We can't even buy most new-release 3D titles now without importing them, and how long will the overseas market sustain 3D? Making 3D possible without the use of glasses is the only way I see the format surviving long-term...