I thought for sure that the Three Tenors used sheet music on music stands, but maybe I'm wrong. I've noticed that most of the operatic vocalists and instrumental soloists that play with our local symphony, do so without sheet music.
In choir, I usually look over somebody's shoulder to see the first word or two of a verse. The rest I sing from memory. I man the microphone mixer, and it's nice not to have a hymnal in my hands.

-Joe-