Continuity mistake: When Daredevil kicks Bullseye off his motorcycle, Bullseye has nothing in his hands when he's flying through the air, but when he lands he's holding Daredevil's baton. Watch closely when Daredevil's kick connects, and you can see they never even come close enough for Bullseye to grab the baton, or for him to snatch it if it was dropped.
Factual error: When Matt Murdock is looking at Elecktra in the rain, he can make out the irises and pupils. This wouldn't be possible for two reasons. Irises and pupils have no depth that could be sensed through his radar sense. Even if they did, he could only see them if the rain was falling straight into her eyes, which would be quite painful and highly unromantic.
Factual error: When Elektra's father is killed, she picks up what appears to be a Glock 19 and empties it in the direction of Ben Affleck. We hear the weapon click a few times indicating it is out of bullets, but the slide is still in the closed forward position, and it should be locked back when it goes empty.
Factual error: Does anyone else find it odd that there were not only one but three window washer baskets hanging on the side of the building? How did the window washers get out of the baskets halfway up/down the building side, jump? Baskets are never left hanging on the building side because 1) it is unsightly and 2) it presents a potential for damage to the basket/building if a high wind or something comes along. They are stored on the roof top where they are secure. They are controlled from the roof or the basket to keep vandals/thieves from gaining access to the baskets.
Continuity mistake: When young Matt is taking a shortcut home and he sees his father beating up a man, he runs away. While he is running, he drops his report card. When we first see him, he is riding his skateboard and not holding anything. [This scene is actually edited from a much longer scene (it is included on the 2004 Director's Cut DVD). Matt was looking for his father at a construction site near the school, and learning he wasn't there, Matt drops his report card into the puddle. This is why, later, he is shown running away with only his skateboard. Still a mistake, but there's why.]