As Giles is announcing 5 minutes until the power circle, the violin player behind him is very obviously 'playing' the violin with the bow 2 inches from the strings.
At about 5:40, the girl in the locker room hears a noise. She says "Is anyone there?" and starts to move along the lockers. She then says "Hello?" while she is at the end of the line of lockers but her mouth does not move.
While Buffy is searching around in the backstage area, there is a mirror in the background of the shot. For a brief second, you can see the reflection of a crew member.
Around 14 minutes and 58 seconds into the show, when they are walking out of the Librarians office, you can see the camera man's reflection on the door's window. After the shot breaks away and comes back you can then see the boom as well.
On the widescreen edition of this episode, 15 minutes and 13 seconds into the show you can see a crew member sitting behind the railing in the background. When the shot breaks away and comes back, they are gone.