In another question on this site I noticed that J. J. Abrams inserts the number 47 into several of his movies. I'm curious about it... Why is the number 47 significant?
To expand on @Gilles answer above:
A writer from Star Trek The Next Generation, Joe Menosky attempted to put the number 47 in all of scripts he worked on. Joe attended Pomona college where the 47 club originated. More about the mystery of 47 here.
JJ Abrams has used 47 throughout his productions: http://www.observersarehere.com/number-47/2009/04/
In Abrams trademarks IMDB lists 'Often makes references to elements of the original "Star Trek" (1966) series'. Although 47 was not in the original Star Trek series it made many appearances in the series to follow. So it can be deduced that Abrams is paying homage to Star Trek tradition by including the number 47 in so many of his productions.
Another thing of note is that in the original Star Trek series: Production #47, is titled 'Obsession'.