It is reported that the fresh air found after thunderstorms and near waterfalls is based on the high air permeability of Negative Ions. Having a healthy concentration of Negative Ions can clear the air of nasty pollutants that cause illness and disease.
Salt lamps have a similar effect to that of an ioniser, in that they release negative ions* (*charged particles) into the air. It all sounds a little backwards, you'd think negative ions would be bad for you - other way around, its the positive ions, released by various airborne pollutants such as smog, exhaust, radar, and microwaves, as well as electrical smog from appliances such as TV's computers, radios, microwaves among others that are bad for you.
My lamp is on 24/7. From what I can calculate, the monetary cost is inconsequential, but the emmissions are approx 11kg of carbon per year. I refuse to feel guilt about it however - we don't watch TV, the appliances we do use have all been selected for their energy efficiency where ever we've been able, and as a rule, we're quite energy conscious. Our power consumption is less than 1100 kwh per quarter and falling (even through winter) as we take conscious steps to reduce what we consume.
Now the science isn't concrete, and maybe it's me just trying to justify it, but regardless, I truly feel the lamp makes a difference to the 'energy' of my home, even if it is just ambiance.
So that is the skeleton in my carbon closet. What is yours?