Yeah it works...sort of.
Tried it a few days ago just out of curiosity. Its just plain old electrolysis, plating some metal by taking the copper of the board. It relies on the copper to be removed to be carrying current, so of course, once a copper area is 'disconnected' from the rest (which is on the +V side) it stops reacting. I did have quite a bit of success in removing a large area around my design, but of course isolated areas, and small traces were left untouched.
So just to say, it does work, but not very well. I used a 12V PSU with a salturated salt solution, it drew a current of 1A. Still took ages. And any immpurities in the solution/electrodes will be effected too, which can ruin the process. So I guess its a carbon electrode for the cathode, pure salt, and a half decent power source.
Addiditonally, this has been used to reduce the amount of ferric chloride needed when etching, also speeds it up. You 'pre-etch' with the salt water method, removing a fair bit of copper, then finish it off with ferric chloride to do the fine bits/isolated areas. Watch out for chlorine and hydrogen though..with a huge powersupply it'll bubble, and we all know what happens when H2 comes into contact with Chlorine. (HCL -> water = hydrochloric acid).
I say try it yourself. As long as you score lines in the board to electrically isolate areas, they should stay intact.
Blueteeth