They certainly greatly reduce the amount of stuff hitting the sides of the rig. Since putting the Husky's on I've seen that the side panels are far cleaner after running though snow and roadside surface water. The door handles are no longer caked with dirt and mud. And if you have side steps (or nerf bars) the flaps really help keep the muck off the front steps.
As far as the fenders, they still are picking up crap, but at a much reduced rate. I still think that I'm going to put some clear bra protective film on the fenders at some point.
I can honestly say I've never seen a rig that can dirty itself better than the H3.
The Huskys however do help out a lot.