Harry Potter and the Half-Blood Prince Questions

What are the similarities and differences between Harry and Voldemort's childhoods?
Why does Dumbledore trust Snape? Is Dumbledore too trusting?
Is trust a good thing in the world of Harry Potter?
Who is R.A.B.?
What does it mean to be "pure of heart?"
Why does Voldemort want to become immortal? What's so cool about immortality?
Should Hogwarts reopen next year?
Does magic have its limits in Harry Potter? What can magic do, and what can't it do? What kinds of magic do we see?
If Tom Riddle's mother hadn't made the choice to die, would he have grown up differently?