It depends on the two jobs. Let's face it, what else is a melee going to do but sit there and cntrl A, maybe WS now and then? Some jobs really don't have much to do. If the exp-gaining job is brainless, then a dual-box PL isn't too bad. If the person is dualboxing say ninja and whm, then there's a problem, as both require attention and only one will get it.