The release date for Kingdom Hearts Birth by Sleep has been something of an oddity up until recently, until Square Enix gave fans some clue, as they announced it would be coming in "January".
However, it looks like they've finally given in and announced a more definitive date, as a Japanese site claims to have the official release date for the game, January 9th, 2010. This is only the Japanese release date though, so there's still no word about the North American or European releases.
Be sure to check out in the future for more news related to Birth By Sleep.
Source: FF Reunion