Carrara doesn't have an adjustable torus primitive, a symmetrical lattice generator, or a rock generator; it can't make Booleans that don't lose their UV mapping information, nor can you leave the material from the negative Boolean in the cutout portion of the positive Boolean.  The manipulators in Bryce resize from any direction for any object, i.e., you can elongate from the top without symmetrical elongation at the bottom (in Carrara, you'd have to convert to a vertex object and manipulate vertices, edges or faces---more often than not resulting in faceting and triangulation of your object coupled with loss of UV information); this feature in Bryce is great for twisting and smashing terrains to create things like overhangs.  Bryce has a wide array of light shapes that can be smashed, twisted, and resized for fantastic effects.  Any material can be applied to a light in Bryce, whereas in Carrara, only picture gels can be applied (although you can do this if you purchase the DCG plugin).  Bryce has nice Fuzzy and Additive regimes for materials in the Materials Room that give excellent results.  Bryce's water and glass materials have always been first-rate, whereas in Carrara, they generally need to be tweaked to the umpteenth degree.  Plus, Bryce has really nice alignment tools and extremely convenient masking functions that I have yet to see in any other program.

And even though I mostly use Carrara now, I still do a lot of terrain shaping in Bryce and export the maps into Carrara.

Even in the shadow of Carrara 6, I'm not ready to banish Bryce from my hard drive.