Nothing.

Stem cell and organ donation are a great resource to the medical proffesion just as long as they are donated and not retained i cannot see how anyone would refuse to give life/a better quality of life to another human the problems only occur when the cells and organs are retained without permission ie the organ retention scandal in liverpool and manchester.

Nothing is wrong with donating at all! I would definitely take a donation if I needed one, and I also donate often.
I donate blood and plasma.

If I could, I would donate blood. Unfortunately I lived in Germany about 12 years ago, right during the time when Mad Cow was breaking out. Because of this, I may have prions in my blood. Obviously, they're not giving ME Mad Cow disease, but that's because I'm either resistant or (most likely) just don't have any. Unfortunately there is no way to test for prions in the blood of living creatures. The only way to tell is to dissect a dead creature and look at its brain. Then, if it has died of mad cow disease, then you can say it had prions in its blood.

So my body is pretty much off the market until I die. Even then, I won't die of mad-cow disease but my organs could STILL have prions in them so I think my flesh is basically considered poison, especially since it's undetectable. Which sucks.

Yikes that sounds scary.

Meh, like I said, chances are I don't have any prions. It's just impossible to test for.

Cool. Thanks for the info.