For a number of years I have used PJ1 Blue Label chain lube with good results. However, it seems every owner's manual (including the one for my current bike) says to use 80 or 90 weight gear oil to lube the chain. The way I understand it, today's O-ring chains are internally lubricated and oiling it merely keeps the O-rings pliable and prevents rusting of the links.
With that said, has anyone tried using heavy gear oil rather than specific chain lube? Perhaps the manufacturers know something we don't -- or don't want to appear to be pitching for the chain lube makers?