Personally, I resent them as spoilers. I wish no fics were labeled, because I hate being spoiled. It really ruins my enjoyment of a fic. I don't want a hint that minor character X is to meet a grisly death-- just kill him, and let me react with proper emotion to the event! If you're writing an AU, kill whomever you want: Aragorn, Frodo, I don't care. (Well, I care, but it _is_ an AU; take it where you will.)

I even resent dropping the name of the pairing, because often that's part of the fun--discovering who will end up with whom. However, I realize that many people want to read only about certain characters or certain pairings, so I always provide at least the major character.

On the other hand, I realize that some people really do have issues with certain kinds of violence or kinky sex. It is polite to warn them, but I'd prefer to warn as vaguely as possible. Warnings about slash or het strike me as simply silly, but then, I write both and read both so I don't have a drum to beat in either arena.

What I do like: the rating, and the genre (humor, drama, angst). That's enough to prepare me for the mood. I can trust a good writer to handle the story and plot elements to my satisfaction, no warnings required. :)