They are not lightest ones out there, as my pair weighs 800 g (28.2 oz) for size EUR 44.5 (US 10.5). However, Salomon's weight distribution concept seems interesting. The XT Wings are said to be the result of tests which showed that the total weight of the shoe is not as important as the weight distribution from heel to toe. Salomon claims that while most shoes have a 50/50 weight distribution, it's definitely better if the back of the shoe could be lighter than the front section, and XT Wings are designed that way.
It's too early for me to confirm any of that yet, but I did a 15K test run today both on asphalt and dirt and the shoes felt pretty good.