I've had people job shadow me before. A few years back I had three people job shadow me on three different days in a row--ugh that was draining! At the end I was asked which one I thought was going to be able to pick up the job quickest and also which would be the best personality fit with the corporate culture.
One woman was very nice but really had a hard time grasping the type of work we did--I showed her several things a few times and she just wasn't getting it. One woman was very bright but by noon her personality was fairly abrasive--I had made lunch plans with a friend in town on business a week earlier, and she seemed miffed that I wasn't able to ahve lunch with her. The last woman was pleasant and picked up the work quickly and asked intelligent questions--she is the one I suggested they hire and they did.