One other thing to mention is that the majority of transfusions given in surgery, usually between 1-2 units, has been found to be inappropriate. A study showed that in two large groups of patients, the blood either had no benefit at all (wasting blood supply), or resulted in negitive outcomes (heart attack, stroke, lung injury, infection and kidney failure, and death).
Hemorrhaging/trauma is a different story, this appears to be the only group of patients to actually benefit from blood. It's this type of thing we need to keep plenty of fresh stock for, and try to use alternatives and better blood conservation methods for other patient groups. That said, I've recently heard that even hem/trauma can now be treated with alternative methods, although, training up medical professionals in all these methods takes time and money.
Group Questions Appropriateness of Most Blood Transfusions