Factual error: When Dave is at the Yankee game and he is telling Linda he wants to marry her from the field, it is impossible for his voice to ring throughout the whole stadium without a microphone (even though it echoes as if he were using one.). Similarly, he wouldn't have been able to hear Linda when she shouts "I'm over here."
Factual error: After the Yankee game when Adam Sandler and Marisa Tomei are going home via the subway, they show Yankee Stadium in the background and they are standing on the platform further away from the stadium. If they live in Brooklyn, they should be on the platform closer to the stadium as that is the one that is south bound towards Manhattan and Brooklyn. The one they are on goes north. Why would they be going north away from home at that hour?
Factual error: When Dave and Buddy get to Boston, Dave is using his cell phone, mentioning that they didn't have to take a five-hour trip to Boston just to find out that Buddy's mom was getting a Jelly Bean removed from her nose. Problem is, he's calling from the ramp staircase of Alfred Lerner Hall at Columbia University, which is in New York City, not Boston.
Factual error: When Dave is on the plane the flight attendant is talking about "how their country is going through a very difficult time right now" meaning the 9/11 attacks but later on in the movie when Buddy is in the shower and Dave is talking to his lawyer on the phone on the roof in the background you can see the twin towers.
Factual error: Adam Sandler's apartment is near the Brooklyn Bridge. His office is in downtown Manhattan since you can see Brooklyn Heights and the Brooklyn Queens Expressway from his boss's office. Jack Nicholson pulls the emergency brakes on the Queensboro bridge when they are heading to Sandler's office. You wouldn't take the Queensboro bridge to go from Brooklyn to downtown Manhattan.