While the characters are recalling the last things they remember before being in the Cube, Geraint Wyn Davies' character, Simon, states he was in New Haven. When the screen divides into different views, the shot on the right/upper right of the screen is an alternate take from another Lions Gate film Davies had a role in, American Psycho II: All American Girl (2002). The similar shot in American Psycho II can be seen shortly after 1 hour 6 minutes into that film.
The trivia items below may give away important plot points.
There is an extended ending (featured on the DVD) in which Kate is told that her total time in the cube was 6 minutes and 59 seconds. If you look at the other characters wrist watches (throughout the movie) it as always around 6:00. This works together with the number 60659 or 6:06:59.
When Colonel Maguire is killed, the effect of the wall of energy crashing into him is actually just created with a vacuum cleaner stuck on exhale (to blow his clothes around) and CGI, for the wall itself.