I think Dec 25 is as likely if not more likely than any other calculated date:
http://www.wnd.com/?pageId=119886
I saw an interesting program on one of the channels about whether the stories from Luke and Matthew were true. It talked about the Christ star that was seen by the Maji. They tried to scientifically decipher what that star could have been.
Chinese records showed no record of any supernova appearances during that time. Comets were ruled out as signs of death - not signs of birth. Alignments of planets and stars were studied as well. But it was the historical implications that led one person to a theory that to me is entirely plausible.
First of all, the people of that area (Judea/Palestine) had no interest in astronomy and celestial showings. So the Biblical account was entirely derived from the mindset of foreigners (the maji). It stipulated that they were probably from Babylon and had come to Judea because they were fully knowledgeable in Messianic prophesies because of their extended contact with the Jews after their conquest of Jerusalem.
This person discovered a coin out of Syria or Babylon that was dated around 27 AD which had an image of Aries looking back over its shoulder at a bright star. So this person studied the constellation Aries during that time and looked for something out of the ordinary. One object stood out as the sign. Jupiter (the Zeus star or king star) was eclipsed by the edge of a thin crescent moon in the middle of Aries during that period. He dated it April 17, 3 B.C. It makes sense to me.
It was also pointed out during the program that in Luke’s account, shepherds were tending their flocks during the night. The only time shepherds would do that is during the Spring.