A growing number of unclad hikers are wandering the Alps, near Appenzell. Some Swiss legal experts say that banning nudity in public would be unconstitutional.
In recent years, it has become fashionable for a growing number of Swiss and some foreigners to wander in the Alps clad in little more than hiking shoes and sun screen. Last summer, the number of nude hikers increased to such an extent that the hills often seemed alive with the sound of everything but the swish of trousers. …
read more in the NY Times – In Thin Air of the Alps, Swiss Secrecy Is Vanishing
I tried it myself on the John Muir Trail in California for about an hour. … Too short an experiment to get “comfortable”.
Fans of hiking in the buff should subscribe to the Nude Hiker blog.
besthike.com 
I imagine it would be difficult to acclimatize. As an avid hiker in Nevada, I can imagine that attempting this would result in the awfulest sunburn.