Fundamentally, I'm not against the idea of a third Hobbit film. I loved the LOTR trilogy, and I'm sure Peter Jackson will do well with the Hobbit. The problem is... the Hobbit is such a short book. I'll admit it's been a long time since I've read it, but I seem to recall it being shorter than any of the single LOTR books. And it was already scheduled to be made into two movies.
To now make it into three movies means things are either going to be stretched very thin, or they're going to need to add a lot of stuff that wasn't in the book (Gandalf's with the Necromancer/Sauron for instance).
Does the story really need three movies, or did the studio just suddenly realize "Holy shit, our cash cow is drying up", the way they did with the end of the Harry Potter series, or that stupid Twilight movie? The franchise is a huge success, and then at the end they turn the last book into two movies just to milk it for as long as they can. And then we end up with something like The Deathly Hallows part 2, where an hour and a half of the movie is Harry and the gang sitting around the woods doing nothing interesting.
If the Hobbit had been announced at three movies, I'd still be skeptical about that single book needing so much movie, but at least I'd feel like "Hey, they've got a plan". Suddenly turning it into three movies, when the first two are already filmed (one of which coming out in four months) sort of makes it feel a little more like "Hey, can we get more money out of this?"
I'm looking forward to the Hobbit. I have really high hopes for it, and I'm excited to see Middle Earth on the screen again. If it all turns out well, shit, they can have my money. I'll see three Hobbit movies if they can fill three films with content that feels like it needed three films to tell. I'll see more than that, if they want to start tapping some of the more obscure Tolkien Middle Earth stuff for more movies.
I don't care if they want more money, really. I just hope that's not all they want.