Unfortunately, this little revelation about a fictional character's sexuality has really made the two sides of the "culture war" more clear than ever. Travis at the Sword of Gryffindor blog recently wrote an excellent analysis of the opposing sides (and he also called that the culture war should stop, to which I say "Here, here!") I strongly suggest you read his post. I also have my own little thoughts.
First, I don't understand all the Christians who are up in arms about Dumbledore being gay. Reading many of their comments, you would think they had wanted any gay character to be overtly negative. Of course, most of them probably would have been content without there being any gay character at all (and so would I). But let's look at it this way. Dumbledore is shown throughout the series as being an outstanding leader, role model, teacher, and overall moral person. He values innocence, friendship, and most importantly, love. Isn't it a good thing to have a gay character show those qualities? I really do believe that a reason many gay men and women lead lives of depravity is because for years society has said that depravity is the only thing homosexuals are capable of. Luckily, I have learned this to be untrue, and even though I think homosexual sex is outside of God's will, I'm fine with there being positive GLBT characters in fiction.
Second, for Bible-believing Christians who now think that the Harry Potter series is not redeemable, I would ask why homosexuality is any worse than the instances of lying, stealing, and other sins that occur in the series. Travis from SoG was very correct in pointing out that many Christians see homosexuality as a sin above all sins, and it annoys him as much as it annoys me.
But even more than that, isn't this a wonderful opportunity for Christian parents to talk to their children about homosexuality? Goodness knows there must be hundreds of gay kids in Christian households who could benefit from this. By all means, despite his sexuality, Dumbledore still seems to live a Godly life. He seems to have lived celibately, and he devoted his life to teaching and fighting the evil of Lord Voldemort. In fact, I would argue that he's a great example of what homosexuals in the Church are called to be. I know I'm certainly inspired by him. :)
Did Rowling mean it that way? Probably not. However, characters are meant to take on a life of their own outside of their author. Christian parents can reap a whole lot of good from this situation. They can teach their children that gay people are not bound for Hell (or even earthly depravity) just because of their orientation. In the off chance that their child is actually gay, they can start a wonderful dialogue. But of course, I'm having the feeling that people really like dialogue a lot less than they say they do, and that's a real shame.