Maxwell: What Allen G said - pressure on the pedals equals resistance to shifting. In theory, you could force the mech to shift without internal damage, but derailleur cables and cable binders are only so strong; much better to let it shift easily when the pressure is off. The advantage here is that the pressure does not have to be relieved for long enough to allow engagement of the next gear, as on other hubs. Rather, any pressure relief allows some shifting, so in extreme situations, you can do many "micro shifts", sometimes two or three per pedal stroke, until the ratio is properly adjusted. As for the fixed gear dream, that would be fantastic, but, unfortunately, it is not possible with this version of the hub. The mechanism itself freewheels, and only engages fully when pedalling forward. The reason for the external freewheel is that the mechanism and the seals give enough resistance that the hub would be prone to "ghost pedalling" if the cog were attached directly to the hub driver. The folks at Fallbrook have admitted that a fixed version might be a possibility in the future. As with any major company, they need to be convinced that the market justifies the research and manufacturing expense. And as for big loads, don't try to tell me you don't have a collection of such stories yourself - or is that a different thread?