Oops! I meant that for you, donh:
Is String Theory physics or metaphysics?
(Bonus Question: Do you believe that gravity is caused by a graviton or is it just curved space?)
Until there is a potentially dis-confirming experiment to be performed, within an affordable budget, I feel pretty safe in calling it metaphysics. Your mileage may differ at different science institutions, but I think most would probably still agree with me--as is the case, for example, with SETI, cold fusion, and crop circle reasearch, whose parallels with the anthropic principle I recommend for your consideration. As with speciation, it's not so clear when the instant is that you now have another science. It creeps up on you. That is also insufficient reason to claim that any problem that tickles your fancy is, ipso facto, science.
(Bonus Question: Do you believe that gravity is caused by a graviton or is it just curved space?)
I have no idea, I'm not even convinced there's a distinction; when was the last time you saw a graviton in the flesh?