And for all the QT fans out there, he has said in interviews that it is a coincidence that a couple of them are. But the person that said there are all but one is wrong.
From IMDB:
"There is a persistent myth that that all the clocks in the movie are set to 4:20 (although, certainly all the clocks on the wall in the pawn shop are set to 4:20). However, in at least two scenes it is obvious that this is not the case. In the "Bonnie Situation" while Jimmy, Vince and Jules are drinking coffee in the kitchen, the clock clearly reads 8:15. Secondly, when Vince and Jules go to retrieve the briefcase, it is "7:22 in the a.m.". The significance of the time 4:20 is that it is slang for smoking marijuana."
Thank you. To purposely disrupt continuity to make a point is one thing (ala the Silver Surfer poster in Reservoir Dogs and Silver Surfer reference in Crimson Tide are put there purposely because he's one of Tarantino's favorite comic superheros), but to have one scene that coincidentally refers to marijuana is just that, coincidence. At best, Tarantino might be making a point about the pawn shop owners (shedding some light on who the characters are), but to assume he's deliberatly making a pot reference because he thinks it's funny and cool is just not the case.
Now, the 666 combination on the briefcase, there's something deliberate for ya.