Oceanic flight 815 is seen breaking up in-flight only a few hundred metres off the ground by Ben and Juliet. However, in season 1, when the tail breaks off, the plane is at cruising altitude well above the cloud layer.
Ben tells Goodwin he can make it to the tail end on the North Beach in "an hour". In the "Other 48", Anna Lucia said Goodwin came out of the jungle 10 minutes after they landed in the water.
When Sawyer gets returned to his cage after the escape attempt, the lock is placed back on the cage as Juliette is approaching, but it never gets snapped closed.
When the Cell is flooding with water and Jack and Juliette are fighting for their lives, Juliette tells Jack to hit the yellow button...but the button he hits is red.
In the opening scene, Juliet is seen putting the Talking Heads CD "Speaking in Tongues" into the CD player, but "Downtown" by Petula Clark is heard instead.
During the book club meeting "earthquake", a stick can be seen knocking over a lamp.
When the cell is flooding, Jack and Juliette manage to close the flooding door. The water pressure forcing the door open is thousands, possibly tens of thousands of pounds of pressure. It would require more than Jack and Juliette to close the door.