Did Paula Abdul, Michael Jackson, Mariah Carey, and Janet Jackson? I always thought they did, but I could be wrong.
I think most artists rely on back up vocals, tracks, and plain lip-syncing sometimes. Maybe it just depends on the event. Mariah Carey's New Year's Eve performance was terribly faked. I felt sorry for her it was so bad. Parts of Michael Jackson's Mowtown performance seemed off. Both artists are gifted singers though.
Christina Aguilera usually performs live. At least she did when she was younger. I attended one of her shows and you could hear her pant when she was out of breath. She still sounded amazing!