Love and Harry Potter
To say, "I love chocolate" usually means, "please excuse my excess intake of sweets." "I love Harry Potter" means I find delight in reading the Harry Potter novels. "I love rock and roll" means you should put another dime in the jukebox, baby. "If you can't be with the one you love, honey, love the one your with" conveys one of the more common usages of the word love in contemporary society. Ellis Paul is correct when he notes that, "Love is too familar a word."
WARNING: There be spoilers ahead!
Love in the Harry Potter series is more specific than the general American usage. When Dumbledore says love is the most powerful magic there is, he is not talking about a warm affection for someone else (though I don't think this element is excluded). The love that is powerful magic is a love that sacrifices. From the start of the series there is proof of this statement - Harry Potter is "the boy who lived." The question is why did he live?
Voldemort pursued the Potters with the intent of killing their son. No one was more feared in the wizarding world than Voldemort. Yet he was unable to kill an infant. The killing curse deflected back on him rendering him helpless and near death. The infant received nothing but a scar on his forehead.
When Voldemort came to kill Harry, he quickly dispatched of an unprepared James Potter, and then offered Lily the chance to flee. Given the opportunity to save herself, Lily instead gave her life in an attempt to defend the child she loved. This sacrifice placed a protective charm on Harry even greater than Voldemort's dark art. Throughout the series Dumbledore reminds Harry that it was his mother's sacrificial love for him that saved him.
This theme of sacrificial love occurs repeatedly in the series as character after character suffers or dies for another, most often for Harry. Until, near the end of book seven, Voldemort gives Harry a choice - come and die, or stay and watch others die for you. Harry knew that to complete the task of destroying the horcruxes he would have to die, so he walks deliberately to his death. Both Lily and Harry's sacrifices call to mind the words of Jesus, "Greater love has no man than this, to lay down his life for his friends."
Harry's love is also shown in a less dramatic way. For so long he had loved and trusted Dumbledore. Now he knows the secrets of Dumbledore's past. He also knows that Dumbledore knew all along that Harry would have to sacrifice himself for Voldemort to be defeated. But while he cannot fully reconcile himself in the short time he has to who Dumbledore was and the plan Dumbledore placed in motion, his love for Dumbledore "bears all things, believes all things, hopes all things, endures all things."
Love in Harry Potter like Biblical love is costly. Snape lives his life constantly being suspected as a traitor by most, especially Harry. All out of grief that he betrayed his one true love, Lily, to Voldemort. While many of his actions are not excusable, how terrible a reminder must Harry have been. The boy who looked and acted like his father, but with his mothers eyes. The boy whose scar was a reminder of Snape's own betrayal of Lily.
But he does what is required of him to protect Harry and the others from Voldemort. Like Harry, he follows Dumbledore's plan even when it does not make sense. His actions are a testimony to the fact that his love was genuine, and his regret real.
So in greater and lesser ways, love displayed in the series requires setting aside personal desires, even personal needs. Lack of love and the inability to understand love I think defines Voldemort even more than his fear of death. So, in Harry Potter as in the Bible, love is not all we need, but without it we are nothing.