Latest TdF doping: what's the dope with Homologous blood transfusions

Vinokourov has failed a drugs test for Homologous blood transfusion Link

From what I read he apparently had a transfusion with another persons blood. What’s the deal here? How does this technique work and offer the rider an advantage? What’s the dope dope?

The idea is that the rider has greater oxygen delivering capability than he would without the transfusion. As to weather or not it provides benefits I don’t really know.