I don't want to be too hard on string theory because in reality I like the theory and hope it is correct. That said, this cartoon by XKCD reminds me of the parallels between string theory and Russell's Teapot:
"The extra dimensions are really there we promise, they are just too small to observe...", "The supersymmetric partners that should exist for every particle are really there we promise, they are just at a high enough energy that they are out of our reach... ", "The 10^500 vacuum states leading to a multiverse...." etc...I guess what I am worried about is that if string theory is not falsifiable in any practical way then you could never know if it is false or not. Like Russell's Teapot.
Now, in defense of string theory, in principle these things may be able to be observed once we have built good enough detectors. Therefore maybe it could somehow be falsified.
I guess another big difference is string theory employes hundreds if not thousands of physicists and the detection of Russell's Teapot doesn't. :)