I agree about not putting Shelob into TT. I think the movie would flow better if it just ends with Frodo and Sam heading toward Cirith Ungol. Since the actual story of RoTK is only a little over half of the book, it makes sense to pad it with the whole Shelob thing. That would be quite a bit of screen time. There's going to be enough going on in TT without that part.
Thanks for the ping, maq!