I'm a gen person too, really; and my gaydar, such as it is, only ever works when it comes to literature. In real life I'm quite hopeless, especially with regard women. Maybe one reason is that I don't care about people's sexual orientation. I like them as a person or I don't; whether they love men or women or both or neither is just not important to me.

I guess that in literature things are simpler than in life. The signals are easier to pick up, and a writer composes a character with a degree of deliberation. In the case of Slughorn (whose existence seems to have slipped my mind when I wrote my post), he appears gay because the historical person on whom he was modelled was gay too. With Dumbledore I had a hunch because he showed several characteristics that I have previously encountered in books and study - very simple things like the fact that he is a flamboyant, eccentric, unmarried scholar who in his position as a mentor to a young boy/man appears in a classic pattern of Greek love. He didn't have to turn out to be homosexual, but he certainly fits some typical (perhaps clichéd) patterns.

Is this important? Well, no. I just have a big grin on my face because at least one of my pet theories got confirmed :-).