At the end, right after Luke comes out of Dr. Squires' building, when he loads the doc's mixtape into his walkman, he has an analogue watch on his wrist, but in the next scene when he puts up his headphones, he has a digital watch.
When Stephanie gives Luke her number, Luke puts the piece of paper in his pocket. When he later checks it out, the paper is neat and without any creases whatsoever.
During the end credits, when listing Olivia Thirlby's stand-in, Thirlby is incorrectly spelled as "Thirby."
When Stephanie offers to help Dr. Squires "tag" his belongings before he moves out, the CD she writes on is "Scarlet's Walk" by Tori Amos, which was released in 2002, 8 years after the movie is set.
On the "honeymoon" the kids take, Faith Evan's "You Used to Love Me" is heard playing on the boom-box. The story takes place in the summer of 1994, while Evan's single wasn't released until 1995, nearly a year later.
As Squires laments on the new New York he quotes Starbucks as an example of the city's Disneyfication. But 1994 was Starbucks' New York debut and they were not yet synonymous with unchecked corporate growth.
The movie is set in 1994 but when Luke returns to find his family being evicted there is a current model BMW 7 series, E65/E66, turning the corner in the background. These have only been manufactured since 2002-2008.
During the scene where Luke and Dr. Squires are walking near Times Square, an advertisement for a Pontiac Solstice can clearly be seen in the background. The production year for this car began after 2005.