Character mistake: When Carrie is describing the younger guy she is dating, she claims he is the creator of an Internet magazine 'that she still wasn't able to find on her computer'; meaning she had searched the Internet for it. But as we learn later in the series, right before she gets back together with Aidan for the second time; she doesn't have the Internet on her computer until then. The girls talk her into getting it, in order to email Aidan. So there was no way she could have searched for the other guy's Internet magazine on her computer, as it was an older Mac laptop and not likely to have search engines without Internet access. She was only using the hard drive at that time.
The real me - S4-E2
Character mistake: Miranda, Charlotte and Carrie are sitting in the cafe waiting for Samantha, when she runs in late, armed with her photos. Just before she'd arrived, a waitress had come to take their order - Carrie ordered a drink but nobody ordered food, but when Samantha offers the photos to look at Miranda says something like "But only till the food arrives." They didn't order any food.
Character mistake: When Charlotte is looking at her wedding announcement in the New York Times, there is a close-up shot of part of the article. It says, in reference to Charlotte: "She is a writer and editor at Fashions Magazine in Manhattan". This is not true, nor has it ever been true. Perhaps the producers of the show threw that in, to see if anyone would notice. Also, the same article mentions: "The bride, who will be keeping her name..." and yet we never really hear Charlotte use the name York instead of Goldenblatt. (00:16:45)