I have shot them off a hard surface, concrete and very dry ground. My groups are larger than when shooting off bags, but I don't know if it is because of the hard surface or because I can't keep the gun as steady when on the bipods compared to the bags and shooting table.
On the shooting table, I can rest my gun on the bags and support myself too. Still, I can get decent "hunting" groups with my bipod.
I have a swivel model bipod and on this last hunting trip found its value when setting up on uneven surfaces.