With the dawnguard DLC, feeding is absolutely useless since NPCs no longer attack starved vampires. You have a pit of thralls in the castle that are worthless unless you want to gimp yourself as a vampire. In the next game feeding needs to be what drives vampires and make them stronger not weaker. It was fine in oblivion because of the sun's effects and NPCs not attacking you when you were well fed. Now there is little use for doing what vampires are well known to do.