I have a friend that has Ortlieb panniers and loves them...said they were good on the boat, too.
He told me that he met up with some Germans cycling cross country. At the campground at the end of the day they filled an Ortlieb with ice to keep their beer cold. They also would fill one with water, soap and dirty laundry, ride a while, then rinse.
Seems like a pretty verstile piece of equipment!