To try to bring together John's post on disliking depressing stories (a perfectly valid point) and Becca's question "What has dystopia done for you?", I'll get a little personal.
Like a lot of people -- like a lot of writers -- I carry around a certain amount of undiagnosed depression. My writing and my depression have a strange, symbiotic relationship, but for now let's just say that I've been wrestling with it for most of my life.
Dystopian stories are depressing, as John pointed out. I would even say that there's a certain correlation between a dystopian society and the inside of a depressed mind. I can attest to the interior harangues, the (self)flagellation, and the sort of numbed haze that dystopian medications seem to induce.
Fortunately, a good chunk of dystopian fiction involves resisting and fighting the dystopia on some level. Maybe the protagonist does not win, but the fight will go on because we've seen one character struggling in the system, we've seen one light flicker to life in the darkness. There'll be more.
Here's where Becca's question comes in: dystopias remind me to keep fighting.
In other flavors of fiction, where people are beautiful and the quest may be tough but there's help to be had and love to be found, it's easier to fight the good fight. And I enjoy those stories, but they don't resonate with a depressive like me the way resisting-the-dystopia stories do.
I was going to recommend Mockingbird by Walter Tevis -- it's a hopeful dystopia, with a post-apocalyptic flavor -- but apparently it's out of print. I got my copy through www.paperbackswap.com. If you can find it in a library or a second-hand bookstore...
...which brings me around to digital publishing and books that perhaps ought to be available as ebooks if nobody can be bothered to print them. I'm still a dead tree reader, but I can see how the wind's blowing. But that's another round robin topic.