With all the spume and nonsense online and in the media regarding embryonic stem cell research, it's actually quite hard to find a sane, well-written, scientific article that explains just why embryonic stem cell research is important. The staff over at blog.bioethics.net seem have found a good example, even if it is rather diluted by discussion of funding and politics:

Although it is true that no one has to date been treated with cellular therapies based on human embryonic stem cells, I can assure you that mouse embryonic stem cells have had a major impact on medical research. Over the past 25 years, mouse embryonic stem cells have been used to create models for scores of human diseases, including cancer, heart disease, obesity, and Alzheimer's. Research discoveries based on these models has led to new drug development and therefore touched countless lives. As for the criticism that no one has been cured with embryonic stem cells, the field of human embryonic stem cell research is a mere 7 years old, so it is premature to expect successful cell therapies to have already been delivered to patients. I believe it is only a matter of time before human embryonic stem cells are used in drug development research and become the basis for important new cell therapies.

As further evidence of how human embryonic stem cells enable unique opportunities to study disease, consider research on Fanconi's anemia. Kids with Fanconi's anemia suffer bone marrow failure, and often develop leukemia. Scientists have tried to model this disease in mice, but the mice do not develop bone marrow failure, and the adult blood stem cells from Fanconi's patients cannot be maintained in culture. Recently, a team from the Reproductive Genetics Institute of Chicago isolated a human embryonic stem cell line that carries a Fanconi's gene mutation. This cell line could enable us to study the uniquely human aspects of Fanconi's anemia.