I have a Jamie Roy and a Steamroller. Between the two, I'd say the Jamie Roy is more "harsh", but I think that is partially a function of its tires. The biggest difference to me comes on rough roads, e.g. ones where the top layer of asphalt has been stripped off for repaving. On these types of roads, the aluminum seems to have much more high frequency (or at least, as high frequency as it's going to get for a bike frame) vibration going through it. When it comes to hitting bumps, I don't think there is much of a difference, though I suppose the steel could take the "edge" off the hit. And to put it all in perspective, my Jamie Roy is never so harsh that it's a problem. I agree with r0cket - it seems like your wheels/tires, bars/stem, and saddle/seatpost "influence" the ride quality at least as much, if not more than the frame.