Hey Cray, this was touched on in another thread, but I think its worth having a thread focus on it.
I myself started both my trilogies with prologues featuring the main charaters as children, covering significant events that had an effect on their later years, when chapter 1 joined them. I thought it was a great way to introduce them, to explain why they are the way they are, and what they fight for.
Since then I have deleted them. I think it is a superfluous vanity that comes from loving your characters, and one that is very hard to hit the delete button on. However, my way of looking at was that there simply wasn't any real reason to have it in there, other than that I wanted to have a prologue like so many other fantasy authors.
In the case of main-characters-as-children at least, it isn't necessary, because if I'm doing my job properly, the reader will come to know who the main characters are, what they're fighting for and why they're doing it. To be so heavy handed in directing the reader as to who they should be paying attention to is a little condescending, in my opinion.
An alternative, however, is to change it slightly. For example, one of my prologues was about a girl (let's say mage, for the sake of this example), who destroys her village as a child, when anti-magic inquisition types turn up looking for her. Because a) I wasn't really happy with it as introduction to my magic system (I was throwing too much at the reader too early) and b) because one of the inquisitor types comes in later, I rewrote the entire prologue from the inquisitor's perspective, leaving the reader to make their own (very simple, granted) consclusion that the young woman they were dealing with at chapter 1 was the girl from the start.
I still deleted it though, because even after all that it still wasn't necessary. That isn't to say such an intro won't be necessary for you, I'd just advise being objective about it, no matter how much you like the scene (and I really liked that scene).
Remember to do what is best for the book!
Now, a brief note on epilogues. I love them, and will always use them. They're a great way to both 'finish' the story, but also allude to the next one. If you think of all the great movie trilogies that do it (Back to the Future, Fellowship of the Ring [though granted, the 'hunt some orc' scene was in the novel Two Towers, but meh], even Magneto's little shiver of the chess piece in X-Men Last Stand), they can lead to exciting cliffhangers-that-aren't-cliffhangers, because they're hinting at more to come even though your main story is effectively 'finished'.
In short, I think prologues can be excessive and go wrong easily (remember, the reader doesn't even know your world yet), but epilogues are brilliant, because the reader is at the end of their journey.
That isn't to say prologues in books 2 and 3 can't be effective though!
Wow, what a load of drivel. Hope it helps.