From The TV IV
The number 47 appears extremely frequently in a number of series, mostly with science fiction elements. The phenomenon began with Star Trek: The Next Generation, continued on to other Star Trek series, and has been adopted in other programs, most notably Alias, and Ronald D. Moore may have carried the tradition over to Battlestar Galactica.
While it's likely that not all of the 47's spotted by fans were intentional, there are enough to suggest that the number isn't appearing at random.
The use of 47 on television can be traced to ST:TNG writer Joe Menosky, who attended Pomona College, where there is a 47 society dedicated to the number, and the belief that there is a proof showing that all numbers equal 47.