I love Luna-logic, she's completely crazy in all the very best ways. I love that Harry has stopped protesting at the end and doesn't try to reason with her - I think that's probably the only way to really deal with Luna.
My only critique is really an opinion more than anything - the way OotP read to me, I think that during the beginning of Harry's 5th year Luna had a crush on Ron, not Harry. It doesn't really matter and this story is pretty cute.