Ulth's explanation pretty much hit the nail on the head. I don't think Twilight being a princess is suddenly going to mean that she'll be sitting around in frilly pink dresses and having tea parties with socialites in her new glittery castle, or anything like that. If anything, I imagine it would involve her going around Equestria, traveling to new places, meeting new ponies, and solving problems with the help of her friends. I think it has a lot more potential for awesomeness than most people are recognizing, basically.
I also think that an alicorn transformation and princess title are a lot more fitting as a destiny for Twilight than most people realize. That's going to be a bit longer of an explanation, though, and it's getting pretty late, so I'm afraid I'll have to put it off for now. ^^;