Other than one laptop disk drive, I've been fortunate on gravel and rough roads. Similar to others, a lot of gear isn't type that would be damaged - or I pack the more fragile items such as a laptop or camera surrounded by softer items such as clothes.

Where I've had more issues is with the panniers themselves or the racks. I had the metal mounting points of my front rack fracture and break (fortunately Surly gave me a new set of brackets after my trip) and also had welds on a rear rack eventually fail. I've had plastic brackets/clips on the panniers also break over time.