Continuity mistake: In season 1 "Valley of the 20-Something Guys," Carrie receives a phone call from Samantha and her voice over says she needs her morning Marlboro Light, however, when she picks up her pack of cigarettes, you can see that it is a pack of Merits.
Continuity mistake: During the scene when Carrie and Sam are in the changing booth at the clothing store, Carrie starts helping Sam take his shirt off. She pulls the outer plaid shirt down quite a bit, revealing his white undershirt. But in the next shot of him, Sam suddenly has the plaid shirt back up around his neck. Then in his next shot, it's back down and the white undershirt is showing again.