During the woman's meeting Kirsten leaves to "check on the thing" during this Julie has her drink in her left hand and a snack in the other, the camera then changes and the items have swapped so that her drink is in her right hand.
When Seth enters Marissa's room and Summer's top is off, you can clearly see a couple of tattoo's on Summer's right shoulder; one of which is a butterfly. Throughout the rest of the series, Summer's right shoulder is exposed many times, however these tattoo's are never seen again on her body. Correction: Kids that age get temporary (stick on) tattoos. This is not a goof.