I'd always suspected it, but it was nice to have confirmation.
And this will finally shut the "ZOMG-JK's-a-homophobe-because-she-made-L
As if the fundies didn't have enough to complain about with the Harry Potter series, this ought to send them into as yet unexplored throes of righteous indignation. Should be fun to watch!
I'm glad that Rowling finally officially outed Dumbledore, because his almost blind following of Grindlewald in the seventh book simply wasn't fully explainable with a mere "best buddies forEVAR" storyline. Dumbledore being in love with Grindlewald makes a lot more sense. Love makes us do incredibly stupid things, "best buddies forEVAR", not so much.
Now she just needs to own up to Minerva McGonagall. ;)