During Luke's rather odd date he is asked who would play him in "The Luke Danes Story". He replies that he's never thought about that, but in fact he has. In the previous season, while visiting a girls' soccer game, Lorelai suggested Tobey Maguire could play him in the movie and he immediately suggested Viggo Mortensen.
When Lorelai and Chris attend the astrophysics lecture, they are clearly not present in the overhead camera shots taken from the rear of the classroom.
When the creme brûlée arrives at the table you are able to see the microphone visible above them.
When Kirk is talking to Luke at the diner he says at 0700 hours tonight he is going to break up with Lulu. 0700 hours is 7:00 a.m.; 7:00 p.m., as he's referring to, is 19 hundred hours (19:00).