When Lawrence leaves the hotel room in New York, to meet with his publisher, he's walking down the hotel corridor carrying his tie and a champagne bottle in his hand, however he doesn't remove his tie or buy the champagne until after his meeting.
When Lawrence and Janet are in bed he asks her a question and she moves her arm above her head. The shot switches and while she's answering her arm is down at her side. After she answers she again lifts it up.
When the congratulatory card slips out of Lawrence's manuscript, it is at about a 45 degree angle from the edge of the desk (roughly from Lawrence's point of view). In the next shot, it is perpendicular to the edge of the desk. This may be more obvious when using the stack of paper next to the card as a reference.
In the exterior New York hotel shots, which were actually shot in Pittsburgh, the taxi used is clearly a City of Pittsburgh cab, used as such in other parts of the movie, not a New York City taxi as suggested by the movie's story. Pittsburgh Cab Company checkers, logo and phone number are all visible on the side of the cab. The cab is also missing the NYC medallion, the medallion number on the roof, and the sub-letter on its license plate, all characteristics of New York City taxis.
Professor Wetherhold would not have been able to see his car being towed from his son's dorm room. His car is parked behind the east wing of Donner Hall (the actual dorm at Carnegie Mellon where the scene was filmed). The only place in Donner Hall from which it is possible to see the car from that angle is the common area of the dorm's 'A' floor, one floor above the parking lot.
Spenser's "Faerie Queene" is misspelled on the blackboard, an egregious error for an English Literature professor. That the camera lingers on the shot may indicate an intentional mistake by the filmmakers.