Here is the link to the last round of discussion about black boxes: http://www.piscatorialpursuits.com/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=1;t=011243#000000

I have one, wouldn't troll without it. RR, you are right the BB does not attract fish the electrical current that naturally occurs when you place disemilar metals in the water is what makes that happen. You don't have to be moving for this to happen, stick disemilar metals in water and you will get a weak battery action. The box just allows you to control that current. The video that comes with the box shows what happens when the current is raised and lowered, the salmon move toward or away from the source depending on the level of the current.
Yoadrian, it is hard to quantify how many more bites you will get with one, what the box does for you is to control the current which will attract more fish into the area of your lures, thus more fish = more biters, that simple. When the fishing is good I don't think it makes a big difference, it's when it's scratch fishing that it makes a difference to me.
Good luck and tight lines, Jeff