Whenever a book has a prologue, I get annoyed and experience the urge to skip right over it. In a prologue, you'll usually learn about an event that takes place long before the actual story does, and you'll meet characters which likely will never be presented again from their own perspectives; thus, upon finishing the prologue and getting into the main story, I feel as though I'm starting the book all over again, armed with a bit of information that usually doesn't make any sense yet. I feel as though I've wasted time learning about characters that may never make another appearance again. To make matters worse, the prologue sometimes won't seem to have a purpose recognizably relevant to the story even after reading quite a bit into the book. Prologues sort of remind me of info-dumps, in that they present too much too soon. They introduce characters that I usually can't feel anything about one way or the other (because the prologue is too short for me to really get to know them) and often a lot of information on a world/system/event/etc., which doesn't make a lot of sense in the absence of the main storyline. I like books to start right from the beginning with the introduction of the main characters and the main storyline. Most of the time, prologues seem like an unnecessary detour, the contents of which could be handled more gracefully via flashbacks, a character's reminisces, or some sort of second hand account during the course of the story.