I've just carried my bike a little over a kilometre on my shoulder. I don't know how those cyclocross racers do it. Okay, so they have lighter bikes (and probably tougher shoulders), they're only doing it in short bursts and they're fired up for racing, but it hurts! Not just the top tube digging into your shoulder – I found it was better to rest the nose of the saddle on my shoulder – but bottle cage in the ribs and (with cables running under the down tube and beneath the chain stay) lack of hand holds.