Blood drives and the entire concept of blood donation may soon be a thing of the past if some British scientists have their way. They're working on developing synthetic human blood that can be manufactured en masse and used on anyone who needs a pint or two.
They'll do this by using embryonic stem cells from type O-negative donors. O-negative blood is very rare, but it's universally compatible, meaning it works in everybody without being rejected. Once they have these donor cells, they should be able to make as much blood as they need, in theory. Of course, they first need to overcome the ethical issues with stem cells, but it appears that this might not be a huge problem much longer.