A toggle that causes checked items to move to the bottom would be helpful. That way done items aren't in the way and it's still possible to uncheck them.
I think the best behavior would be items staying in the order of the original list when they're moved to the 'done' section at the bottom, not the order in which they were marked done. And the currently selected item should move to the next or previous item on marking it done, not follow the item down.
A toggle that causes checked items to move to the bottom would be helpful. That way done items aren't in the way and it's still possible to uncheck them.
I think the best behavior would be items staying in the order of the original list when they're moved to the 'done' section at the bottom, not the order in which they were marked done. And the currently selected item should move to the next or previous item on marking it done, not follow the item down.