I got to go to a special advance screening of The Hobbit last night thanks to my mother-in-law. It was some sort of official thing put on by this company they contract with, so there was some pretty sweet swag
Overall, LOVED IT. I haven't actually read the book (I know, I know), so I can't really compare it to that. But I thought it was great.
Some general things:
1) I don't know if you heard, but after the New Zealand premiere, some people were complaining about the 48 fps causing migraines and physical illness. I didn't notice any of that, but there were a couple scenes where the camera was moving very quickly and cutting sharply at time. That did cause me to have to glance away a couple times.
2) The running time is about 2:45, so make sure you pee before the movie starts. ;-)
And now, a couple movie specific things ( aka spoilers, unless you've read the book )