The best advantage is that many animals are genetically quite similar and far more numerous, so considering we have chronic organ shortages its a feasable way of making this up. It's a bit twisted though IMO:
Here's a rather disturbing picture of a mouse with a human ear grown on its back. Apparently it will survive when its taken out.
Details here.
PBS has a good website section on the whole
xenotransplantation issue.
[ 03-25-2005, 08:03 AM: Message edited by: shamrock_uk ]