I can speak from personal experience that it absolutely stinks to have the ending of an HP book ruined. I accidentally stumbled across info about the big death in OOTP a few days before the book was released.
Of course, part of that was my own fault for poking around the Internet, but had I realized that the plot would be spoiled, I never would have read that post on another message board (if the thread title hadn't been so innocuous, I would have skipped it).
I don't think we're being bossy, just protective of our members and lurkers.
Once we hear that "Harry lives" or "Harry dies," that's the end of the suspense from reading the book. There are some sites (one very large Yahoo Group, in particular) that are shutting down for a certain number of hours after the book is released in the UK.
