Factual error: At the very end of the film Bruce is reporting on a drive for blood donors, and Grace leads him over to the booth to give blood himself - he is even wearing a tourniquet. However, he is supporting himself on a walking stick - he is not fully recovered from the injuries he received when he was run over, which happened when he was hit by a moving car - injuries which left him clinically dead. There is absolutely no way that a person who has suffered life threatening injuries and has undergone the (inevitably) intensive drug therapies and surgical procedures involved while under treatment in hospital in the fairly recent past would be allowed to give blood. There is no way that the Red Cross (or the US equivalent) would want to encourage people who have recently been hospitalised to try to give blood. Not only would that be the height of irresponsibility, they would be wasting precious resources and staff time turning away people who would not be allowed to give blood.
Other mistake: Early in the film, Jim Carrey is watching TV during a sports segment. He is watching Channel 7, the station he works for. This clip they showed was of actual WKBW sports director John Murphy. The clip they showed was taken directly from a real WKBW newscast, with the authentic news set, and graphics. However, when they show a clip of Ch. 7 News later, there are completely different graphics, and a completely different news set, both made for the movie.
Continuity mistake: After the riot in the streets of Buffalo, Bruce meets up with God again in the Omni Presents building. They discuss how everything is going wrong. At the close-up shot of Bruce's face when he says, "What do I do now?" the frame is flipped. You can tell this because his hair is parted on the wrong side and his nose looks different. (01:15:20)
Continuity mistake: When Jim and Jennifer are in the kitchen and Jennifer is commenting on how she thinks her boobs have gotten bigger, Jim is squirting ketchup onto his plate. When he first does this the ketchup goes everywhere all over his plate, cuts to Jennifer and then back to Jim and the ketchup is now in a nice neat pile. (00:44:30)
Revealing mistake: In the scene with the accident, the car already has bumper damage just before it hits the pole. (00:21:00)
Visible crew/equipment: When Bruce goes back to the building toward the end of the movie looking for God and finds it deserted, as he runs through it, you can see the shadow of a figure (a crew member) on one of the columns on the left. It even slightly moves as he's approaching the ladder as if trying to duck away from behind. (01:13:55)
Factual error: Even God could not arrange for everyone to win the lottery at the same time. Many people use their favourite numbers, and many syndicates play the same numbers every week. There is simply no way - God or no God - that every ticket could win, because there is no way that every lottery ticket could be the same. The tickets cannot have been magically altered - many people know the numbers they have played and would not think they have 'won'. Note that the protesters are complaining that they won the lottery but got back less than they paid for the tickets they purchased. That is only possible if everyone who bought a ticket won, as all lotteries pay out a percentage of the total amount of money taken in from ticket sales.
Continuity mistake: In the diner, Bruce is looking out the window and the waitress walks up to him. You can see the two coffee cups on the side of Bruce's table next to each other. When the waitress asks "Coffee?" and the shot changes, one of the cups is suddenly at the centre of the table. (00:31:15)
Continuity mistake: When Bruce has just smashed his car into the pole, he throws the prayer beads into the water and says, "The gloves are off, Pal," which is confirmed in the subtitles. Yet when God reads back what Bruce said from his file cabinet, God reads, "The gloves are off, God." (00:22:40 - 00:29:45)
Continuity mistake: In the scene where Bruce is confronting the gang that beat him up earlier, he has the monkey come out of the guy, who falls to the ground in pain. After the other guys run away, there is a shot of Bruce taunting them, but the injured guy is not on the ground behind him, even though he should be visible. A second later, he reappears when Bruce turns to face him. (00:38:35)