Cheers to J. K. Rowling for acknowledging that Dumbledore is gay. Jeers to her for not writing him as gay.
Then again, what is there really to write about? His sexuality isn't at all important to any storyline in the books; including it would be an obvious political statement (of sorts). In a word, unnecessary.
I've always had an inkling that he could be gay; an old, beloved educator who was never married nor had any children. The possibility is just staring at you in the face.
Too bad it wasn't touched on. In fact, it's too bad Rowling didn't write any gay characters into the story. A pair of lesbian witches in flannel robes and mullets would have been sweet; especially if they were part of the Order.
Speaking of which, I don't remember Sirius Black ever dating a woman...
Also, Leaky Cauldron's transcript of J. K. Rowling's Carnegie Hall Reading here.