If this isn't the best example of what NOT to wear when you're all dressed up and need a jacket to flip on top of your dress so you don't freeze in a very cold northern hemisphere winter, I don't know what is.
Yes, blazers have been worn with great success to formal functions, but this isn't a blazer. It's like some kind of long tuxedo jacket. And to be honest, I don't think it's ever seen another piece of clothing that it would be friends with - I wouldn't even wear it with pants. It's so looooong.
I'm sure because Uma's tall (about 6 foot I've heard) she thinks she can get away with such a long hemline. But just because you tower over the rest of the population doesn't mean you can defy the laws of balance and proportion in the style arena. It might not be an exact science, but it's a science nonetheless.
Fashion fail. Which is unfortunate because it's such a long time since we've seen Uma out, you really want to see her looking good!