I have often thought that it would be a good idea if the manufacturers of panels were required to put labels on the cover of the electrical panel that said something like "CAUTION modificcation or maitenance of this system other than by a qualified electrician may result in electric shock or fire and could void your homeowners policy." In a lot of cases it wouldn't do any good but for some it might make them think twice.
As far as a shared neutral, as long as the circuits are identified in all locations accessable then it would be a okay but I think it can become a problem when several branch circuits are in the same junction box. In most installations it isn't a problem but I have seen it in larger custom homes.
