Prologues can be great, if they're done right. Personally though, I don't like the ones that are too distant from the story (in time or place), or which feature characters that aren't in the story. So distant past or future scenes are out. And I'm getting kind of tired of the trend in fantasy to demonstrate how history repeats itself. Whether it's because it's handled badly or is simply overdone, I don't know. And I might be in the minority with that opinion.
As yet, I don't think any of my stories have prologues. If they did, they'd be two or three pages of actual story/world introduction, setting out the necessary information about politics and the rules of the world (if there's something like magic in it). If a reader isn't willing to invest in a meagre three pages, then they can just go pick up another book. Preferrably one with pictures.
