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.
Any episode in which the focus is Steve's never-ending quest to get laid but always coming up short is a winner in my book. I liked the idea of Steve becoming too attached to his clone-girl to actually want to have sex with her.