DON'T detune. Thats just stupid. Sure it will help you with rails but it will hinder you going off tables and doing turns and shit. Seriously man having tuned skis is the way to go. plus the skis will naturally dull out if you do rails.
i'm used to skiing with dull edges underfoot, i don't necessarily like it better for rails, I'm more concerned with my new edge ripping out. But maybe with my new pair I'll keep them tuned up, if that's not going to put them at greater risk for damage.