Not long ago, Writer Unboxed had a "Flashback Feud" (read parts one and two). They lay out some interesting points.
Flashbacks, when people ask me about them and where I stand on their usage, are one of the things that make me sigh. There's no short answer.
Well, there's a very short answer -- don't use 'em unless you have to -- but it leaves a lot to be desired. For instance, what "you have to" means.
It's also a matter where my training conflicts.
My academy based education has a certain love of what I call strange usages of time, which encompasses the flashback, nonconsecutive parallel stories (like the one discussed in part one of "Flashback Feud"), the nonlinear story (i.e. a bunch of really fucked up flashbacks). And then there's all the time bundles that people often declare their love for. I love that it all happens in the span of one day / hour / year!
The notion here is that if manipulating time adds to the cool factor, then dude, you've just added to your cool factor.
My Odyssey Writing Workshop education taught me that a writer should be wary of the flashback, like a person with acid reflux is wary of the hotsauce. That it's one thing to sneak in the past via dialog or through a carefully placed line of exposition (go easy on the exposition or it'll give you heartburn too), but if an event is important enough to put into scene, then it's probably important enough to put into scene chronologically.
There are really extremely interesting, beautiful mindfucking things an author can do with well-developed, well-placed non-chronological scenes. (The Hundred Thousand Kingdoms, which I just read, is a great example of this.)
But for most stories, jumping around in time is doing the story a disservice.
Life unfolds chronologically (unless you've got a suped up DeLorean you're not telling me about). Therefore it's the story form that has the most verisimilitude. So the distinction then becomes whether the story serves the artistry or the artistry serves the story.
If the work showcases the story, then don't do something that draws the reader out of the immediacy of the story like flashing back into another time in place.
If the story's purpose is to showcase the writing technique, then do whatever you want.
In the past year, I've had several people (people who've never met each other) say to me why not just put it in chronological order? It was like a little light bulb went on. Or perhaps a whole series of them. Suddenly I was not walking down a dark and twisty path, but hanging out in a well lit neighborhood. Things were nowhere near as daunting to write (omg, the where do I put that scene? factor drove me nuts when I went un-chronological), but they also appealed more to my readers.
As far as my own writing goes, I try very hard not to include flashbacks these days.