> When handing out references of something bound with let mut, why do i need to do &mut instead of just & ?

Sometimes, you still want to immutably borrow a mutable variable. Otherwise, you wouldn't be able to have multiple references to a variable declared with `mut`, which would be an unnecessary limitation.

EDIT: Here's an example of something that wouldn't otherwise work if borrows of mutable variables were implicitly mutable:

    struct Point {
        x: i32,
        y: i32,
    }

    fn add(p1: &Point, p2: &Point) -> Point {
        let x = p1.x + p2.x;
        let y = p1.y + p2.y;

        Point { x: x, y: y }
    }

    fn main() {
        let mut some_point = Point { x: 1, y: 1 };
        some_point.x = 2;

        // `some_point` is borrowed twice here, which wouldn't be possible if the borrows were mutable.
        let other_point = add(&some_point, &some_point);

        println!("({}, {})", other_point.x, other_point.y);
    }