In interviews, Kal Penn revealed he originally had a much greater role. It would have been revealed that his character was a disgraced former Daily Planet science reporter who was bribed by Lex Luthor to plant false evidence of Krypton's possible survival, thus inspiring Superman to leave Earth and explore Krypton's ruins.
(at around 40 mins) Superman's line, "It's still the safest way to travel", is a reference to Christopher Reeve's comment in Superman (1978) after rescuing Lois from the falling helicopter. "Well, I certainly hope this little incident hasn't put you off flying, miss. Statistically speaking, of course, it's still the safest way to travel."
When Bryan Singer became interested in possibly hiring Brandon Routh, he arranged for them to meet in a coffee shop. When they met at their table, Routh stumbled and spilled hot coffee all over the table. Although he panicked, thinking he had just lost the part, Singer laughed and said it actually helped him get the part. The incident convinced Singer that Routh could pull off the clumsy, bumbling Clark Kent.
The last line of Superman IV: The Quest for Peace (1987) is Superman saying to Luthor, "See you in twenty." That scene was filmed in 1986. Coincidentally, twenty years later, this film was released.
Jack Larson: (at around 26 mins) Jimmy Olsen from Adventures of Superman (1952) appears as a bartender who serves to Clark and Jimmy.
Michael Dougherty, Dan Harris: (at around 57 mins) the two writers of the screenplay make an appearance as school kids making notes as Lex Luthor arrives to steal the meteorite and shoos them away.
Guy Hendrix Dyas: (at around 1h 40 mins) Production designer: one of the journalists of Daily Planet, who first notices the tremor at the building.