Has anyone read the fake Order of the Phoenix book? The one where Harry gets some sweet lovin from Hermione? Even after I figured out it was a fake, I still read the rest of it, because it was so well done. Of course I also read Half-Blood Prince, but not until WAY after it came out, and I had already found out "the BIG SECRET".
IMO, any person who believes the entire point of reading the book can be ruined by hearing bullshit tidbits like "snape kills dumbledore" has worse problems than a spoiled plot point.
Of course, any book that CAN be spoiled that way (and HP6:H-BP ISN'T) should be burned anyhoo.