It would be great if Lightroom 4 had GPU support for CUDA enabled video cards similar to the Mercury Playback Engine in CS5. That would really speed up performance! Every couple of seconds helps when you are editing 1000s of files.
Saving 2 seconds between images comes out to be an hour of saved time when you are editing 2000 images. I have 12 GB of RAM, and 12 core processors at my disposal and sometimes i have 4 seconds between images.