I've built a couple of them and love them for the kids or for hauling gear. Better than a backpack if you're traveling over flat terrain (eg. frozen lakes) and have a decent load. Big hint if you have kids - get the folding camp chairs (the simple ones that are just a seat and back) and bolt them into place along the sides of the sled. Kids' slippery snowsuits on plastic sled = kids all over the trail. Also, some extra hook bolts along the sides always help for lashing things in.
It's truly easy to build them, and mine were built for <$35 (excluding camp chairs) in a short time. It's amazing how often I get stopped when out snowshoeing or skating by people who want to see how I did it.