They also won't accept you as a donor if you have any kind of auto-immune disease (because we still don't know how it works and if it can be transfered via blood cells or marrow), and generally, your body has to be in good shape.

I thought about donating but my doctor discouraged me and advised me to take it serious, e.g. don't lie while filling out the donation forms. Even though it probably would turn out fine someone could die because of you which is exactly the opposite of what you've signed up for.