Precisely, Spidervlad. That is the million-dollar question, and one seemingly worth a lot of speculation and theories.
From what we've gathered from the narrative and the dialogue during the final confrontation, Harry's sacrifice removed the permenancy and binding from Lord Voldemort's spells. Harry -- and the book -- mention how Voldemort is unable to completely hold the crowd in silence. Harry then boasts that Voldemort will no longer be able to kill any of them, even should Harry die. What is the extent of this?
Are we to assume that he is referring to the Killing Curse? Death is, for most people at least (excluding Harry and Voldemort), binding. So does Harry's sacrifice refer only to the Killing Curse -- in essence, had he removed its finality? Should, say, Voldemort attempt to use it on a student, it wouldn't work? This seems to be the best idea that I can come up with, given how the Cruciatus Curse no longer had its ultimate effect, and Neville was able to eventually break out of Voldemort's Body-Bind hex after his brief torture.
But, as we saw, even after Harry's sacrifice, Voldemort was not rendered powerless. Though his Silencing Charms were unable to hold the crowd, they did so for a while. After one broke, he did succeed in shutting them up with "another, stronger" curse. And still, Harry was forced to use Shield Charms on those whom Voldemort attacked as the Death Eaters were forced back into the main hall.
So, what were the final effects of his sacrifice, exactly? Did it merely render the Avada Kedavra curse obsolete? Because Voldemort was still capable of harming and potentially killing his enemies -- he just had to use a variety and plethora of spells -- forcing Harry to try to protect them with shield charms. Lastly, Voldemort was still capable of overpowering three supremely powerful wizards who had the advantage of not being affected by Harry's sacrifice (in that they could still kill him).
Any takers?