One of the many reasons why the first half of the Deathly Hallows blew every other HP movie out of the water so badly as to make you wonder whether the same people had made it, was its great take on Harry and Hermione's friendship - but in the book like in the movie, while the friendship makes sense, it's also clear that it's platonic.
Ron and Hermione works on some levels, but as to whether it works in the long run - well, as Larry mentions, that really depends on how they'd evolve in young adulthood and beyond, wouldn't it? If, like most characters in the series, they don't seem to evolve much anymore after leaving Hogwarts, in any way, then sure, why not. At the time of book seven, which ultimately is the only thing we can really discuss, I think it makes more sense than Harry with Hermione. Of course, Hermione with some random other guy whose interests align more with hers could also have made sense, perhaps more. But Harry is hardly that guy, either.
I did like Harry and Ginny, it had that inevitability issue hanging over it admittedly, but Rowling's attempts to give Ginny her own personality from book five onwards while Harry was elsewhere with his thoughts romantically, worked out quite well I thought. Of course if you compare to YA books where the romance and the character development is the focus (like, say, the genius of Aidan Chambers), Rowling's romances all feel a little flat, but considering how they have to fit into the epic story, I'd say she does a commendable job of it on the whole. In the end perhaps it's a little Eddings-esque with the way the protagonists neatly pair up with each other, but at least you've got things along the way like Hermione's relationship with Krum to shake those clichés up a little.
With the romances, she did a better job with the core of the series than with the epilogue, that's for sure. Harry-Ginny and Hermione-Ron worked as teenage couples. Ginny-Harry sounded like the type of relationships that could actually mature and endure, but Hermione and Ron had many earmarks of being a first love that would peter out sooner than later. I can't really think of a character in the series that would make a likely partner for an adult Hermione. So if Rowling missed the boat, for me it's perhaps by an unwillingness not to show Ron and Hermione no longer together as adults. Harry and Hermione wouldn't have worked any better for me.
For much of the series she offered her non too subtle caricature of the suburban conservative mindset to which she opposed her more whimsical and excentric Wizards (cheating by having a whole lot of non conformist adult Wizards at the forefront of the story.. from Dumbledore to Hagrid, several teachers, Sirius and Lupin, the Weasley dad etc., the conservative ones from "the establishment" showing up as "bad guys" only later). Yet by the second half of her series, she scratched beneath the surface and started to criticize more and more a much deeper conservatism and inability to face necessary changes among the Wizards themselves (splitting them between the pro and anti Dumbledores). It was a little disappointing indeed that with the epilogue she showed her young heroes simply falling back in line with the old order. It's like her message is that only youth dare think differently and as soon as they're adults it's like a disease and they fall back in line, which I'm pretty sure wasn't her intent. It's more like she forgot her criticism of the conservative Wizards after the non conservative ones won against evil, and has not given much thought to how the Wizarding world should chnage in an era without Dark Wizards.
It's not that I expected her to bring massive changes to Wizarding thinking, it would have been unrealistic, at least in the short space an epilogue left her to elaborate on that. I guess it's really more a case where less is more and there was something to be said for an open ending without any epilogue set years later, leaving individual readers to decide what happens next...
