
Question: If I understand correctly, Lily Potter's "love" protection no longer keeps Harry safe after the graveyard ritual, due to Voldemort getting some of Harry's blood. Why, then, doesn't Voldemort attack Harry at the Dursleys' house in the summer?
Answer: Voldemort's spell undid the Sacrificial Protection that Lily bestowed on Harry, but the Bond of Blood is a separate protection bestowed if the person sacrificing their lives is a relative. THAT spell is still renewed as long as Harry keeps returning to the Dursleys until age seventeen. Voldemort has removed one protection, but a second is still in place.
Captain Defenestrator