Character mistake: When talking to a family, Christina says that the patient had "hematomachrosis" instead of "hemachromatosis"
Character mistake: Christina pronounces the dead patient's condition incorrectly. She says Haemotomachrosis. The condition is Haemochromotosis.
(As We Know It) (Part II) - S2-E18
Character mistake: Meredith states that she cannot remember the last time her and Derek kissed. Derek says that the last time was when they were still dating, but it was actually at the end of season two episode three, after Addison arrived in Seattle and Derek and Meredith had stopped seeing each other. (00:40:00)
Suggested correction: She is referring to the last time they kissed without any issues. The last time they were good.
The Heart of the Matter - S4-E4
Character mistake: Ms. Bitzer says she's booked a trip to Iceland to experience the sun never setting. While the sun does set quite late there, Iceland is located south of the polar circle and does not have midnight sun. And either way, season four has been established as taking place after summer, so there wouldn't be midnight sun anywhere.
Superfreak - S7-E3
Character mistake: When Meredith adds Amy's name to the board for Derek's surgery she spells Amy's last name differently than Derek's.