Personally, I prefer to include still-in-print books, the idea being that if someone is flipping through the current book, sees the bio, goes "Aha! I have been wanting to read about kicking people!" (I write about martial arts), I'd like that person to go buy a book that will put a royalty in my pocket.
That said, I can't see any great harm in including an out-of-print book as long as it is directly relevant to the book in hand or is a book the reader is likely to know.
Jennifer Lawler