For fun, I decided to play a piano duet at home with my daughter. My wife was pressed into service turning pages, despite not knowing how to read music. During the performance, I discovered that she had no experience at all being a page turner, because she didn't pick up on the standard "piano nod" that signals that it's time to turn the page. Fortunately, I had my part mostly-memorized (and my daughter had completely memorized her part), so we managed to complete the exercise without incident.
Anyway, this got me thinking about the art of page-turning. I found A Page-turner's survival guide which sets the ground work for the mechanics of serving as a page-turner. Additional mechanics are spelled out here, including general guidelines like always following the performers on and off stage and not accepting applause unless invited by the performer.
During my undergraduate years, I occasionally served as a volunteer usher at the concert hall, and for one of the recitals, a fellow student was selected to turn pages for the solo pianist. I don't know if I could have handled the pressure.
While searching for information about page-turning, I discovered Pauline Oliveros's Trio for Flute, Piano, and Page Turner (1961), in which the page turner, in addition to serving the nominal role, also assists the pianist by silently holding down keys to raise the dampers (so that the strings can resonate when the pianist strikes harmonically-related notes), reaching into the cavity to effect other sound alterations, and even changing places with the pianist briefly.
I wonder how this affects standard page turner etiquette, such as the rule against accepting applause. Unfortunately, I cannot find any videos online.
Obligatory page turner hero story: Page Turner Rescues Sonata from Sudden Failure.
Bonus chatter: I attended a performance where the piano soloist used a tablet computer instead of sheet music. She turned her own pages by tapping the screen. (Related.) When I mentioned this, my nerd friends speculated how this could be improved through the application of even more technology: Maybe the performer wears a special ring that they can tap with their thumb to turn the page. Or the computer listens to the performance and turns the page automatically. But I told them they were all working way too hard. The tablet can simply be remote-controlled by an assistant offstage who is watching for the tell-tale head nod from the pianist.
Bonus bonus chatter: One of my friends from college is now an orchestra conductor. (Different college friend, not the page-turner friend.) He says that many musicians are converting to digital sheet music, but he sticks with paper. At least for him, paper is easier to read, especially when he has only a fraction of a second to glance at the score during a performance.
Bonus bonus bonus chatter: One of my relatives attended a concert where the soloist used digital sheet music. Unfortunately, something went wrong with the tablet and it wouldn't turn on. There was a bit of a delay while the performer went backstage and returned with… paper sheet music.