To be honest, I can't remember that much of the book, so I'm excited to see how Jackson's version will play out.
I can totally understand him adding some girl power to the trilogy - face it, Tolkien was a bit stingy with female characters, and these days people want to see girls getting in on the action. I'm sure Jackson won't do a complete Mary sue with her though (sorry for using that geeky term, but it seemed appropriate for this subject!) I mean, he was originally going to have Arwen joining in the battle at Helms Deep, and Liv Tyler even did a bit of sword training for that scene, but it was all left out in favour of having Arwen as an emotionally strong character rather than a physical warrior, which rightly went to Eowyn's big moment against the Witch King.
But the Hobbit doesn't really have anything to match up to Eowyn's battle (as far as I can remember) so they'd need to take some liberties.
But I am really looking forward to the spiders.