Yep, on a more serious note...but only slightly more serious.
I've got Ducati hard panniers. Like HW say's they unclip from the bike in seconds and then you have the panache of a Ducati suitcase as you walk into where you're staying.
My panniers have proven watertight as well but stuffing everything into ordinary plastic bags or bin liners just gives that added piece of mind that if they did leak you wouldn't have to go down the bar with soggy boxers.
Can't see any point in paying big bucks for a more luxurious option.