I read prologues. I start a story at the beginning and read through it to the end. I assume the prologue is there at the beginning for a reason, or it wouldn't be there. I assume that if it's simply background information about the world or its history that "might be nice to know but not really needed," it would simply be placed in an appendix. If the prologue is interesting and well written and hooks me into the story, I keep reading. If I liked it well enough to finish it, I'll read the epilogue as well.
If the prologue bores me or has all this strange, panoramic, "zero point of view" omniscient narrative, or reads like a history lesson, or is something I can't follow, or includes characters I don't really care about in the first place and who are clearly just there to be killed off in order to illustrate some "ancient evil" or nefarious plot at work--ugh. I usually stop reading the book unless it's been highly recommended, is by an author I trust, or is a sequel to a book I already really like. I don't assume it will become a proper story once the "meat" of the novel starts. I assume an author would write his or her prologue in the same style as his or her novel. If the prologue is a birth scene and it features a much-longed-for son (or daughter) who has special powers and is ripped from his or her grieving mother's arms by some priest/priestess or wise old sorcerer, my cliche alert goes off. Whether I continue to read will depend on how well and convincingly the scene is written.