New Scientist Whatever happened to machines that think? - Features
If you believe humans think (debateable, interestingly), and if you believe humans don't contain supernatural elements (souls ), then humans are biological thinking machines. Hence thinking machines. Since humans routinely create humans, we can create thinking machines.
So the interesting question becomes, can humans create non-human thinking machines, perhaps a mixture of the biologic and abiologic?
I bet yes. But, just as with Peak Oil, I can't say when. Probably within 100 years.
I tend to think it will be a very bad thing for my grandchildren, but that's just a hunch. I hope it won't be a very bad thing for my children. If I thought a 2nd Christian/Muslim Fundamentalist Dark Ages would delay this development, I might be a Bush supporter.
Alas, the competitive advantages of thinking machines are so great I can't imagine anything short of the annihilation of all human civilizations everywhere significantly delaying their appearance. That is 'destroying the village in order to save it' -- so I don't support the Bush/bin Laden agenda.
 Philosophical arguments against "strong AI", such as Searle's "Chinese Room", are essentially arguments for the existence of the soul, and thus for the existence of a deity. So "strong AI" debates, like the Fermi Paradox are "big question" topics.