Yes, according to J.K. Rowling. She said it during an interview today.
I hope it's true. That just makes the books that much more interesting and controversial. People will go through the entire book looking for "Larry Craigs" (references to him being gay, I made that term up)
Here's the link
I guess it is true! How exciting. I'm such a big fan of those books and read all those other books about the HP series and none of them ever said anything about Dumbledore being gay! That blows my mind. There are more details in the link.
Here's the link