Global Illumination sold me. I do lighting in the real world, and my mind's eye sees in radiosity, not in ray-tracing. I always had to work around this in Bryce with hundred-light globes around the scene, radiosity-fakers near bright objects, etc. The thing I miss most about Bryce is the materials...fabulously rich and very easy to work with. I'm waiting for the Carrara proceedurals and presets to come up that mark. Since I still own both, I'd do a strictly landscape pic or certain kinds of highly-textured abstract in Bryce....and reach for Carrara every time I care about the lighting.