The real idea with stem cells, is to figure out a source in an adult body, or how to trick specialized cells to become stem cells again. Taking cells from another person to grow an organ (or to a less extent, tooth) isn't ideal, because of compatibility issues.
The ultimate goal is to do something like this: You need a new liver, so some fat is exacted from your body. The fat cells are coaxed into a stem cell state, and then directed into becoming a liver, which is then implanted (not transplanted) in place of your failing one. There will be no need for anti-rejection drugs, because you body will accept the liver as its own.
