It came down to the 11th hour, but both Variety and Hollywood Reporter's websites are saying that BL has been picked up for a 5th season. I think the negotiations had to do with ABC buying out "Life on Mars" from David E. Kelly, and in exchange, Kelley wanted at least another season of BL.
From what I've read elsewhere, it's a full-season, but ABC has the option to trim it down to 13 episodes.
EDIT: Crap, forgot an icon. Can somebody with the power to please throw the Lost icon up? This was apparantly shown at Comic Con. It for a station called The Orchid which seems to have something to do with mammalian genetic engineering type stuff. Dr.