When Dawn sings (during Sweet's song), "No you see, you and me wouldn't be very legal," she's twirling in a dance, but during the words "wouldn't be," her mouth is not singing when she turns to face Sweet.
Tara runs into a pole in the Bronze while she is performing her back-up dance to "Something to Sing About." While the pole is not visible in the shot, Tara bumping into something before she goes out of frame in the background is noticeable. Likewise, if you look closely, you can see actress Amber Benson desperately trying to suppress a laugh as she straightens out her wardrobe after bumping into the pole.
During "I'll never tell" after the second dance, Xander and Anya go to sit down. You see Anya sit fully on her chair and slide herself back again, then when it cuts to her face and she begins singing "He's Swell" she's lowering herself onto her chair again.
When it shows a close up of Lethe's Bramble in the book, the blossoms were pointing to the left and beneath the description. When they show a different angle, the flower is facing the other way and on top of the description.
Just after Buffy beats up the three goons, the gang rushes in, but when it skips back to Buffy, they're not in the doorway. Then it skips to Sweet, then back to Buffy. Still no gang in the doorway. Then it skips to the gang in the doorway.