The only thing I can think of the spell being used was in the OOTP when Harry was in Snape's memory seeing his father using the spell on Snape. Other than that I can't think of a time he used the spell. I was also thinking, Slughorn purposely gave him the HBP's book, knowing he would figure it out or something...
Well I'm not really sure, he loves it at Hogwarts, but with Dumbledore dead, he might no like the idea of going back their. But I have the smalest feeling he'll go back their for a short time. Which that leads into my theory of Dumbledore. What if he isn't really dead? Did people actually see his body, and what if the tomb was empty?[PHP]Which that leads into my theory of Dumbledore. What if he isn't really dead? Did people actually see his body, and what if the tomb was empty?[/PHP]