It's my feeling it's generally not allowed. I've often gone wild camping, but do my best to find a local to ask if it's ok. They generally give a bemused look as if to say, 'if you're daft enough, go ahead...'

One particularly nice - although not terribly isolated - place is around Quinten on Walensee. Apparently it's the warmest place in Switzerland owing to the huge cliffs of the Churfirsten mountains right behind you. As there are no cars there, it's quiet and the odd day-tripper / hiker has to take the last ferry back. The lake is only ever a few metres away and affords a great, peaceful view. Use your Primus, though and watch out for the wild pigs scavenging in the night