Killing Characters

I have always hated it when you get really attached to characters in a book just to see them killed off. I am really attached to my own characters in The Blood War Chronicles and have debated this question. To kill or not to kill? That is the question. Anywho, I have debated with a couple of my main characters. Should I kill them off? If I were a reader reading my book, would I get pissed off if this character dies? Should I mess around with deaths of main characters at all? What about secondary characters? I just wonder how other people feel about main character and secondary character deaths.