You guys are all missing the point of the rate button. Obviously you can't use the rear LCD to judge sharpness, but images are supposed to be about content, right?
The rate button is perfect for flagging the images where you captured that big play or that perfect expression. Not images that you have deemed technically perfect based on the rear LCD, but for prioritizing the order of reviewing the technical quality when are sitting in front of a monitor. For sports guys where time is at a premium they can flag the big plays for the editor to review. It would be equally useful for wedding or portrait shooters so that when they get time to look at the images a day or two later.
Also don't forget that the 'stars' don't have to indicate quality. For example, a wedding photographer might have a system where any rating indicates a possible keeper and the number of stars indicates whether the shot was before the ceremony, during the ceremony, at the reception or a formal portrait.