I've been riding the Sram Torpedo hub on my Crosscheck for a month or so now.
The Torpedo hub lets you switch from fixed to free by turning a screw inside the drive side axle.
The hubs been working fine, the freewheel mechanism is way better for winter than a shitty bmx freewheel (you can go through several of those in a Minnesota winter, and there are many legends of people having to piss on low end freewheels to unfreeze them at low temps. This is why so many of us ride fixed in the winter, it's simply the most reliable and practical system for winter bullshit)
Back to the hub, it's great and all. There is a little play that feels like chain slack in the fixed mechanism but it's not really a problem. What I don't really get is what this hubs mission and purpose is. I've got a ton of hubs that you can ride both fixed and free. They're called flip flop hubs. They're significantly lighter, cheaper, and ride fixed without any feeling of slack. This hub costs a decent chunk of money and will freehweel great, and run fixed accpetably. I will give the Torpedo points for it's nice freewheel mechanism, but it all just seems kind of unnecessary.
What I would like to see is a 135mm disc version of the hub, that seems to me to be the best application for this technology. One of the bummer things about fixed mtb ing is that if you want to run a rear disc brake you have to build a separate wheel. For most folks riding fixed off road full time isn't a great situation so they need multiple wheels. If you had a Torpedo style hub with a disc on one side you could easily switch from fixed to free as the trail conditions demanded. Now that would be sweet.