When the pool on the roof "springs a leak", you hear a sound effect for an "impact" type sprinkler. This is the type you would use on your lawn or garden with the little arm that slaps back and forth to move the head, and they have a very distinct sound due to the way they operate. Fire sprinklers have fixed spray heads with no moving parts, and can not make that noise.
When Dade first enters Cyberdelia, there is an overview shot of the whole place, and for a moment we see Joey and Phreak on the top balcony talking around a table. The problem is, this is the scene from the next day. You can tell by the clothes they are wearing.
We see Kate kissing Kurtis on the bike outside Cyberdelia. In the background we see, Crash, Phreak, and Joey walk up and stop. In the next shot, Crash and Phreak are in different positions and Joey is still walking up.
When Dade gets tricked into going to see the 'Pool' on the roof of the school, right after he walks out of the door, he turns back to the door and turns the door handle completely. In the next shot, he can barely wiggle it because it's locked.
In English class, Kate is seen underlining her quote from her mother's book on the chalkboard. After the teacher reads Dade's quote, and Kate says that he is not supposed to be in this class. In the next couple of shots there is no underlining under her quote. Also the exclamation point at the end of the quote has black chalk used as shadowing, Kate is clearly only using white chalk.
New footage of Joey being arrested appears in the film before it happens. If you pay close attention to the scene where Cerel, Freak, Nikon, and Crash begin to watch "Hack the Planet." You can clearly see Joey being led out in cuffs in the background.
Several scenes show the Met Life building (with "Met Life" in huge letters) behind Grand Central. However, the old stock "sky view" footage right before Dade's first day of school shows the building with its original "Pan Am" signage, which was taken down ten years before filming.
When Kate and Dade are walking beside the river on their date, you can clearly see Kate's intricate eyeliner/eye makeup. Yet when they are swimming in the pool before her head goes under and her face gets wet, it has all disappeared leaving just her eye shadow and no smears.
In the "Hack the Gibson" scene Dade steps out of his phone booth to the one in front of him to answer Plague's call, which is the same booth occupied by Burn who is present before the phone rings, disappears during the call and then reappears again after.
In Cyberdelia, as Dade starts playing the video game after Libby moves out of the way, she stands behind Dade to his right. Yet, in the next scene when Curtis asks if Dade is bothering her, Libby is behind Dade to his left.
In Cyberdelia, as Dade's score is appearing on the high score list, we see his score "crush" the fourth and third place scores on the high score list. The camera then shows him looking at his score while two more sounds of "crushing" occur. This should put him in first place, however, the camera then goes back to the high score screen where his score "crushes" the second and first place positions. Thus, the error occurs in the existence of the sound of "crushing" while the camera is not on the high score list.
In the scene when Acid is showing-off her laptop, they speak of the laptop having a processor called a P6 and a PCI bus. Further examination of this scene and another scene with them looking over the damaged code, the laptop that Acid-burn has is clearly a Macintosh Powerbook 280C (sub-notebook) made by Apple Computer Inc. This model does not have a PCI-bus, or a P6. It does have a Motorola 68030 33mhz CPU.
When Kate is describing the specs of her machine she says, "It's a P6 chip. Triple the speed of the Pentium". Dade then says, "Yeah. It's not just the chip, it has a PCI bus". Kate says, "Indeed. RISC architecture is gonna change everything". The P6 chip is a CISC design, not a RISC. Also, the Pentium has a PCI bus so there wouldn't be any reason to mention it.
The P6 processor, which was not yet released at the time of filming but which later came out under the name Pentium Pro, was only twice as fast as even the slowest Pentium processor, not 3 times as Kate claimed.
When Dade is introduced to Lord Nikon, he asks if anyone knows who the Hacker Acid Burn is, but no one knows. Later at Kate's party, the same hackers that said they did not know who Acid Burn is, are calling Kate "Burn" as though they were aware of her hacking handle. However, they are lying because they didn't know who was asking and they didn't want to reveal Kate's identity and get her into trouble.
When swimming in the rooftop pool at the end, Kate and Dade's ears are underwater as they talk to each other. They would still be able to hear each other speak, since water transmits sound waves just like air, albeit somewhat distorted to the human ear. Their voices would be audible to one another, just not as clear as if they were completely out of the water.
Hackers is set in NYC however in the "Hack the Gibson" scene Plague places a call to Dade in Grand Central Station but the phone rings using the European tone (ring ring - pause - ring ring) rather than the American tone (riiiiiing - pause - riiiiiing) indicating that this scene was either filmed or sound recorded in the UK.
In the opening scene of the plane flying Dade and his mother from Seattle to New York, the plane's tail clearly shows "757" on it, indicating this is likely Boeing stock footage of the plane (and not a commercial airline). Additionally, the cabin shot shows 2-by-2 seating, which is not accurate of the economy class plane seating configuration (which is 3-by-3) unless they are in first class. Based on appearances (narrow seats) and coordination with the described economic situation of the mother, them being seated in first class is highly unlikely. At the end when "Mr. Babbage" is flying to Japan, the plane shown is clearly a Boeing 727. The flight attendant tells him the flight time is about 14 hours. A 727's range is about 2700 miles, and cruises at about 615 mph. Simple math would tell you that a 14 hour flight was not feasible with this plane, which is logical since the plane was always considered a medium-range aircraft.
At school when Dade is looking at Kate's profile information to promote himself to Adv English, Dade's school photo is shown in the new window that is opened on the computer before Dade enters his name.
As Dade opens his soda while taking over the TV station with his computer, the viewer can see that the phone is on the hook, and Dade's modem (the box in front of the phone with two rubber acoustic couplers) is unused, yet proceeded to get into a "hacker battle royal" with Acid Burn.