I think Emily Post would have loved Harry Potter. She raised two boys, and told wonderful narrative tales herself. I can say with all certainty that she wouldn't have thought it good manners to wreck the ending for anyone. Spoilers are already out there, and will be especially hard to miss once the book has been out for a few days--or even just a few minutes. Personally, I plan to avoid the internet until I'm done, so please forgive me if I disappear for a little bit. As I'm sure this one will be as good as the others, I'm hoping to be done late on Saturday (frankly, I doubt I'd be able to sleep once I start!) I know I'm going to have a hard enough time not reading the last page myself; I certainly don't need anyone else blowing it for me!
So I'll be direct here. In your enthusiasm to talk about Harry Potter, be considerate. Don't give away the ending. Instead, ask someone first if they've finished. And ask neutrally. If Harry dies, don't ask in a tear-choked voice that leaves no doubt as to the outcome. I hope he lives, but no matter what the ending is, I want to enjoy it in my own sweet time.