Garden State (Natalie Portman)
Elizabethtown (Kirstin Dunst)
500 Days of Summer (Zooey Deschanel)
I think it's pretty clear the kind of character MPDG refers to: on the up side, she's up. REALLY, up - she's perky and fun and playful and usually succeeds at getting our depressed hero out of the doldrums where he can learn many valuable life lessons and be a happier, better person in the end. On the down side, since the MPDG is basically a tool where the writer or director gets rescued by some cute, fun, hot chick, she's has as much depth as a very thin crepe.
I've been feeling conflicted because I feel like I'm my Hades guy's MPDG and I haven't been sure that that's a good thing. But after some thought, I've come to the conclusion that there's nothing wrong with the trope itself - in fact, tropes are our modern day archetypes. Obviously, no one is just a single trope, anymore than they're a single archetype - we're too multifaceted to be compressed into something so one dimensional. But they do speak to things that are true.
I think the only real problem with the MPDG is with the way she's been written. NO ONE is that happy all the time. And no one exists only in relation to one person. Why not show the Pixie while she's at home, washing her hair, or arguing with her mom over her latest tattoo. Or show her unsure and angry, or sad, or scared - not even Manic Pixies are manic all the time. In fact, if Manic Pixies are Persephone's, as I think they are, then you're going to have some crazy emotional crap going on on a regular basis. Which may scare emotionally immature boy writers who want to be rescued and not have to deal with a real human being, but it would make for a much more interesting, and more powerful, story. Maybe they can rescue each other. Or help each other rescue themselves!
So now I don't feel so bad about being a Manic Pixie Dream Girl to my dour (or so he thinks) Mr. H.