Mid Development Medium Shift: Zombieland was originally imagined as a TV series. However, when all the networks the creators went to shot it down, eventually the duo settled on making a movie out of it. The above-mentioned "Zombie Kill of the Week" is pretty clearly a holdover from the TV idea. Ironically, now that the movie has proven a hit, the creators are considering making a TV spinoff.
In the DVD extras, it's revealed that Abigail Breslin liked the zombie makeup so much that she asked the producers if Little Rock could become a zombie at the end. They turned her down.
The sequence with Tallahassee making a last stand is riddled with continuity errors: Look closely and you'll see that he starts out with a 1911 and a P226, then midway through the fight the Sig changes into a P228, and by the end of it he's dual-wielding two 1911s. The whole scene looked cool, so nobody cares.