Well, my first thought was that it doesn't rule epiphenomenal consciousness out. It's strange that people would still talk about consciousness without it, but you can posit that people are just programmed to talk about consciousness for some reason (it's at least conceivable).

Then I looked at the next guy's answer (asparisi) and thought he had a point: Does our theory of causal links allow for causes to have probabilistic effects? (It's different to say that 'human brains sometimes cause consciousness than to say 'human brains can cause ANYTHING, like a blue goblin appearing in front of you or the universe being destroyed and replaced with another one') I'm not sure. If it does, then epiphenomena-that-sometimes-don't-happen are okay. If not, they aren't.

THEN I thought, but if consciousness is an epiphenomenon then what's strange is that people talk about it at all -- by definition, we cannot be aware of an epiphenomenon. But there could be another cause for the discussion of something we can't interact with in any way. After all, people's talk about gods is not caused by gods. There are other reasons to rule epiphenomena out, but a world with P-zombies is at least conceivable, even if it requires a lot of unlikely assumptions.