In the past day, I've run across two related theories of how all of Quentin Tarantino's films are part of the same universe: this video and this post on Reddit. They differ slightly but the Reddit one is more interesting...specifically that Pulp Fiction, Reservoir Dogs, etc. take place in the aftermath of Inglourious Basterds and its unorthodox ending to World War II.
Because World War 2 ended in a movie theater, everybody lends greater significance to pop culture, hence why seemingly everybody has Abed-level knowledge of movies and TV. Likewise, because America won World War 2 in one concentrated act of hyperviolent slaughter, Americans as a whole are more desensitized to that sort of thing. Hence why Butch is unfazed by killing two people, Mr. White and Mr. Pink take a pragmatic approach to killing in their line of work, Esmerelda the cab driver is obsessed with death, etc.
You can extrapolate this further when you realize that Tarantino's movies are technically two universes - he's gone on record as saying that Kill Bill and From Dusk 'Til Dawn take place in a 'movie movie universe'; that is, they're movies that characters from the Pulp Fiction, Reservoir Dogs, True Romance, and Death Proof universe would go to see in theaters. (Kill Bill, after all, is basically Fox Force Five, right on down to Mia Wallace playing the title role.)
Nation's Pride is a fictional Nazi propaganda film that appeared in Inglourious Basterds. The six-minute clip above was released as a promotion for IB and was shot by Eli Roth, who played the baseball bat-wielding Bear Jew (and is also a director of some repute). (thx, jeffrey)
Tarantino's latest film is about Nazi-killing American soldiers and stars Brad Pitt. I can't decide if this movie is going to completely suck or be really great. Vampire movies notwithstanding, Quentin always gets the benefit of the doubt from me so great it is.
A band of U.S. soldiers facing death by firing squad for their misdeeds are given a chance to redeem themselves by heading into the perilous no-man's lands of Nazi-occupied France on a suicide mission for the Allies.