Good question. I am looking for something that can help me catalog and organize photos. I would like to assign key words and be able to sort and make choices. For editing I go to PS.
Well, if you don't shoot RAW and plan to do extensive post-processing in LR, you might want to take a look at iphoto. It can do all the things you are looking for. Organize, rate, keywords. And a newer, even more powerful version should be right around the corner with iLife 07.
One plus of LR: if you send your pictures from LR to Photoshop, it automatically stacks the PS'ed version with the original - no need for you to manually import it again.
Hope that helps.