I really hate back cheats. If you're going to kill someone, it should matter. I have seen a couple of good ones (Sherlock Holmes I felt worked but then I always knew it happened so maybe it doens't count. Buffy was usually quite good at this actually, when it did it) but quite often, it's just annoying and cheap and makes you feel that you wasted a huge amount of emotional energy. I prefer dead to mean dead, on the whole.