I think with all writing concepts, there are no simple answers. Flashbacks are no different. Just as you can ruin a book with poorly constructed multiple POVs, so too can you ruin a book with flashbacks. It all comes down to how and when you do it.
Case in point: I am currently reading Tobias Buckell's The Apocalypse Ocean, the fourth book in his Xenowealth series. One of the POVs in the book is of a woman born from genetically augmented stock by an alien race known as the Nesaru. But the only way we can really understand what her past means to her in the present of the novel (after the events in Ragamuffin, in which a human revolution against alien control had its first and most important victory) is by flashback. Buckell could tell us her history in an infodump, but the result would lack the emotional impact we need in order to sympathize with the character.
Thus, Buckell uses the flashback. Only rather than shove it in the middle of an important sequence, he uses it as a way to further the plot point (specifically, her plot) -- it occurs in a chapter devoted specifically to her reaction to a previous scene; we know something will happen in this chapter, but we don't know what, and so Buckell uses this flashback as a way to show her motivations as an individual. It's a smart move, I think, since it avoids all the problems that can come with flashbacks -- pulling the audience out of the story, destroying pace, etc. It also helps that readers of Buckell's work will recognize familiar themes in this flashback, which might not be something to be expected in other works with such devices.
That's really all it comes down to. If you're going to use a flashback, you have to use it with the awareness of its impact on the rest of the narrative. If inserting a flashback will hurt the pacing or if it appears in a pointless moment in the story, then you're probably going to run into problems.
What I'm curious about are those books which experiment with the flashback form. One example that comes to mind is Brian Francis Slattery's Lost Everything, in which much of the story meanders through different points in the character's lives. Think of it as a long series of interconnected flashbacks. Much of his writing follows this format, including Spaceman Blues. But what other kinds of experimentations are there? Do they work?
Feel free to leave a comment!
(Question suggested by Paul Weimer on Google+.)
P.S.: One might also consider The Testament of Jessie Lamb by Jane Rogers as a kind of flashback-infused text, though that's difficult to argue since most of the book takes place in the flashback, rather than in the "present."