This past summer I attempted to use my bike to deliver a couch to Goodwill without success. Shortly after the embarrassing experiment, they released this thing... which would have been perfect. The trailer is well thought out and just as well built. If not for hauling kids, this thing would probably trump the Xtracycle for hauling stuff.
The biggest benefit is the fact that you could use it on any bike, then just take it off. Take for instance, my Cross Check. It could be used as a commuter, touring bike, and with this, a cargo bike. I could seriously get away with only having one bike. Now, you could say the same about owning an Xtracycle, but their size is cumbersome at times (large crowds, elevators, indoor parking).
For now, though, with the little ones, I'll need to stick with the Xtracycle. And to be honest, I love how many accessories Xtracycle offers with their Free Radical. It gives it limitless capabilities... other than hauling a couch :)
Get out there.