This is the first episode since the pilot that didn't center on one individual character for the flashbacks. Instead, we get flashbacks from Michael, Walt, Kate, Sawyer, Jack, Sun, Jin, Shannon, Boone, and Sayid, all showing what each one was doing before they got on the plane.
Only one third of The Black Rock was built. The rest was CGI.
During filming of the first season finale, each cast member was only given the script pages of scenes where they appeared.
Michael, standing on the almost ready raft, gives instructions "no, no, no, that one goes there, that one goes there" pretty much quoting Han Solo atop the Falcon in The Empire Strikes Back.
Leslie's last name is Arzt. Arzt is the German word for physician or doctor. In the previous episode he mentions that his character in fact has a doctor title (he is a science teacher).