I have a SnowClaw and use it often - but generally for ultralight snow camping where I'm not really going to do a whole lot of digging. It works best digging hunched over, with the snow flying out back between one's legs. It's definitely not better than a real shovel for one's back, especially when digging out pits and trenches.

If you're serious about building igloos, snow kitchens and the like, consider something more like these:

http://www.bdel.com/gear/shovels_overview.php

I have one of their models with the snow saw add-on (it fits inside the handle). We've used it to saw blocks for making windbreaks for tarps while snow camping in the Tahoe area. I also have a Komperdell shovel that's only about a pound in weight, but its shovel is smaller and so I tend to either take the SnowClaw or the Black Diamond, depending on conditions and trip goals.