This situation is unfortunate. Bush is foolish on so many levels, but mainly in the fact that other countries will get the jump on us if NIH is not properly funded to begin research. Bone marrow transplants (aka adult stem cells) are incredibly painful and extremely limited in variety of function. Adult stem cells are what is called "unipotent," which means they can only differentiate into one type of cell at a time.
Embryonic stem cells are "pluripotent," which means they can differentiate into all types of cells, from muscle to neuron, to germ cells - eggs and sperm. They are the mutable macro-building blocks of an organism, but undirected by its genes.
So, adult stem cells are undifferentiated cells residing in differentiated tissue, and therefore limited; while embryonic stem cells are undifferentiated cells in undifferentiated "tissue," and potentially limitless in capability to replicate, well, anything for anyone.
If you take nothing else with you from this post, consider this: embryonic stem cells are taken from a literal ball of cells (the blastocyst, below) in such an early stage in life that it remains unattached to the uterus. No nervous activity, no "parts," only cells.
This is another scientific issue dragged into the political arena, like evolution and climate change, discussed and debated by people who don't even understand (or want to understand) the real science behind the curtain.
All is not lost, however. State institutions like Johns Hopkins in Baltimore was recently given the go ahead by Ehrlich, and $15 million was given to Hopkins for research. And Maryland is not the only state that is bypassing the federal government. We'll get there eventually; then maybe we can save some lives and make some technical headway.
Hopefully I can tie this post in with a discussion of Hox genes when we tackle part IV of "Why Spiders Aren't Insects."