When Jack and Roger are talking to each other in a classroom, Jack is erasing the blackboard. He has erased two-thirds of the content when the shot cuts to Roger. It cuts back to Jack and the blackboard is completely erased, even though he did not have enough time to erase it all.
Miles, who grew up near Los Angeles, tells Hurley he was waiting "on line" at the cafeteria, something no Californian would say. Saying "on line" is rarely heard outside of the northeast and is particularly associated with New York, where actor Ken Leung is from.
The beer cans Kate and Ben's dad are drinking out of in 1977 don't have the old-style removable ring pulls - they have the modern open and fold type instead.
When Jack is talking to Ben's father in the classroom in 1977, there is a periodic table on the wall behind them. The chart contains man-made elements that were not synthesized until 2000.
Hurley claims that Luke overreacted when he found out Darth Vader was his father and got his hand chopped off. If he had really seen Star Wars: Episode V - The Empire Strikes Back (1980) 200 times he would know that only *after* Vader cuts off Luke's hand does he reveal that he is his father.