jon writes:
Even if they're just not looking hard enough?
I think you are confusing matters. There is no concept of an unspecific god, only specific god suggested by specific people.
So when some people say "god created the world in 7 days" and you look and find that the world was not created in 7 days, you have evidence to contradict their god.
Lets compare it with something else. If you are asked to prove there is no milk in the refrigerator, you open it, and look inside. If there is no milk this is evidence of absence of milk.
Now if you claim the existence of a god and you make claims like the one about milk. That is, there is some difference in what we would expect to see in the world should your god exist. If we do not not see these things predicted by your god hypothesis, then this is evidence against you hypothesis. In this way absence of evidence is indeed evidence, just like the milk that isn't in the fridge!
If you suggest a god that is undetectable, then it cannot be falsified, but neither do we have any reason to believe you. I can think of a 100 entities whose existence would be undetectable, but my guess would be that you would not choose to believe any of them.
I can recommend that you read Dawkins "the god delusion". He argues against the popular notion of gods, that is personal gods that act in the world, and specifically deals with difference between thos and the transcendent gods that have no effect on the world. The first class can be shown to not exist with good confidence, the other kind are just irrelevant to everyday life
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