1. As mentioned previously, soft-proofing.
2. The ability to use a 3rd party sharpening solution, especially for output sharpening, such as Photokit Sharpener.
3. Do away with file size limitations. It seems silly to have to go into Bridge to see all of my files. For all of LR's cutting edge features, this completely escapes me.
4. Ability to show image dimensions in inches, instead of pixels in grid view.
5. Ability to show image size in megaBYTES, instead of megaPIXELS in grid view.
6. Fix the thumbnail rendering problem. Everytime I exit LR and re-open, all my thumbnails are pixelated in EVERY folder. I have a cutting edge PC; yet it takes MINUTES for the thumbnails to sharpen up.