Does God change?

Historically, one of the attributes of God that provided the most comfort to many people was his unchanging nature - God is "the same, yesterday, today, and tomorrow." (Hebrews 13:8) Additionally, Malachi 3:3 says, "I am the Lord, I do not change." and Numbers 23:19 reminds us that God is not a man, and thus does not "repent". This doctrine of God's immutability gave solace to those, frankly, frightened of a changing world. On the other hand, there are places where God "changes his mind" (Exodus 32 / Numbers 16) and even "regrets" making humanity (Genesis 6:6 - translated repents in the KJV!) but fundamentally the question is this: Does the God of the Bible change and grow, as say, a progressive theologian (or is that process theologian I forget!) would maintain, or is God's constancy his defining characteristic?