Although this is not made clear until a later episode, the girl in McGee's apartment is his sister, Sarah. The actress playing her is his real-life step-sister, Troian Bellisario. Troian Bellisario's father is Donald P. Bellisario, one of the creators of the show.
One of the college kids in the courtyard is seen looking at the homepage of the Scarlet Secret website. This is a call back to Forced Entry (2004), where Abby infiltrates the company to gain access to their servers.
Jon Wellner also plays on CSI: Crime Scene Investigation (2000) as a lab tech. He talks about forensics throughout this episode and even says "Brass wants answers" - Brass is the name of a detective on CSI.
The music in the background while Abby is playing with the paintball gun is the theme from Peter Gunn (1958).