There are many people out there who still think of Hathaway as the real-life Disney princess from "The Princess Diaries" and "Ella Enchanted", but she's shown in recent years that she's grown beyond that image. She took a dark turn in "Rachel Getting Married" (an incredible, but uncomfortable, performance) and went very risque in "Love and Other Drugs". I think she can draw from both types of roles to be the perfect Selina Kyle -- Catwoman's mild-mannered alter-ego, so to speak -- but it remains to be seen if she can bring the right element of danger to the costumed role. At the least, she's got the body for it.
Then again, the release from Warner Bros. specifically mentions Hathaway playing Kyle, without ever mentioning the name Catwoman. It's possible, given the M.O. of Nolan's "Batman" movies, that the character would spend most of the movie in a non-costumed form, not donning her familiar persona until late in the film (a la Ducard/Ra's in "Batman Begins" and Harvey Dent/Two Face in "The Dark Knight). The same press release did also confirm that Tom Hardy -- who'd previously been attached to the movie, but hadn't been given a role -- will play Bane.
If Bane is done right -- that is, NOT turned into a mute or near-mute hulking idiot behemoth -- than he would be an incredible villain for this final movie, moreso than Catwoman, who has spent so much recent time in the Batman universe skirting the line between hero and villain that it's hard to really call her the latter anymore. Still, the idea of Hathaway slinking around Nolan's Gotham in a skin-tight catsuit... well, that's just awesome.