How much weight savings? How difficult was it?

the bottom part of the back seat is easy as hell to remove, but it weighs nothing.

the top part is just a couple of bolts and undoing a cable, not hard to remove, and it weighs a decent amount. Just remove the corner bolts that you can see when you fold the seat down, and undo that cable that goes to the trunk's seat-fold-down handle.

If you look, you'll see exactly what I mean.