Revealing mistake: When the taxi goes over the edge to capture Dr. Neville, you can see that the underbody of the car as it goes over is a flat painted surface and not the underside of what should be there (i.e., muffler, gas tank, etc.).
Factual error: Neville shoots the propane tank in the kitchen, driving the darkseeker out into the hallway. Shooting a propane tank without an external source of ignition or a tracer would simply result in the tank's gas escaping and maybe the tank moving across the room. The Mythbusters needed an armor piercing rifle bullet to get through a tank and couldn't ignite it even with tracer rounds. Propane tanks are very thick walled. Bullet sparks are a movie myth. Bullets are either lead or lead in a copper jacket. Neither will spark when hitting metal.
Revealing mistake: When Dr. Neville first approaches "Fred" at the trap, we see the taxi from both sides as it sits on top of an intact railing. When the taxi starts to teeter over, there is now a section missing in the bridge that was cut out for the car to fall properly off and be at the right angle to "teeter" as well.
Continuity mistake: At the end of the movie, when Neville is behind the glass and he is thinking and all the sound goes away, you can see the bite mark that the zombie gave him. While the shot is changing between him and the zombie, you can see the bite mark change sides of his shirt.
Continuity mistake: When Robert Neville sees Fred at the end of the road and is lured into the darkseeker's snare trap, before Neville actually gets caught and hung upside down (approaching Fred from the truck and shooting at him), the position of the sun in the sky, and angles of light in the scene, change dramatically in only a few minutes time.
Factual error: When the monsters breach Neville's house, in the scene where one of them is tearing up the ceiling while Anna and Ethan hide under the cabinet, Neville runs in, grabs what appears to be a Beretta M9/92f type handgun, and proceeds to shoot the monster several times. As he delivers the final "kill shot" the handgun is in double action (hammer is down). Unless Neville manually de-cocked the hammer, the weapon should be in single action with the hammer back, from the previous shots fired. (01:25:00)
Continuity mistake: During the scene when the dogs are let loose to chase the injured Dr. Neville, the beam of sunlight is first 1-2' wide, then about 4-5' wide when the dogs try to cross, only to go back down in the next shot to about 1' wide.
Factual error: At the end of the movie when Neville is shooting at the darkseeker, he runs out of ammo and you hear repeated clicking as if the gun kept trying to shoot. He has an M4 and continuing to pull the trigger will not result in a click each time. You'd have to pull the charging handle each time you pulled the trigger to get a click.
Factual error: The scroll on the news reports the Patriots beat the Giants for the second time in the season. This could never occur unless the game was the Superbowl, as an AFC team never plays an NFC team twice in the regular season, and NFC teams and AFC teams do not play each other in the playoffs. The dates do not match up to the Superbowl, held in February.
Audio problem: During the scene where he is hitting golf balls off of the ship, he is hitting an iron. For anyone who plays golf, the sound that goes along with this is that of a driver or some type of fairway metal.
Continuity mistake: Just before Neville goes into the bank with the creatures and instructs Sam, "So look, if I'm not back by dark, just go.". The camera show Neville reaching for the dog, it changes perspective and you can see Neville reaching again. (00:31:30)
Audio problem: Just after the lion takes the deer Neville was hunting at the beginning of the movie, his watch alarm goes off to signal that it's getting dark. The watch alarm in the movie is a "beep-boop" two tone. As the owner of both watches Neville is wearing, I know that the watch we get a closeup of, a Swiss Army Sportech 4000, has a single (once per second) alarm beep and the watch on his other arm, a Hamilton Khaki X-wind, does not have an alarm. (00:07:30)
Continuity mistake: At the beginning of the movie when he is driving his Mustang, the movie is shot inside the car several times. If you look carefully you can see that the same background scene has been used twice. In the scene, you see a red wall from a building and a grey car standing along that red wall. This scene is used twice.
Continuity mistake: In the scene were Robert Neville is hanging upside down from the trap that he walked into, he starts to bleed at the back of his head after hitting his head on the floor. However, the next day when Robert shows Anna his Bob Marley CD, there's a shot of the back of Robert's head after he turns the volume up, an there is no cut, graze or wound visible. (00:46:40 - 01:14:20)