I actually liked Sam a lot in the movies. I didn't get any sense of fat and brainless. He was a bit heavy, but he was actually the closest to hobbit-shaped as Tolkien envisioned them, I think. He generally didn't come off as stupid as much as uneducated, and he had that intelligence of the heart and trueness of spirit that I loved so much in the book.
I do think that he's too violent to Gollum, though. Most everyone is, in the movies.
I guess that perhaps distrust isn't interesting unless someone acts on it?
