eden vs. heaven

Summary "Humans were not complete/sanctified in eden."
So I was wondering what the difference between eden and heaven would be. I mean, eden was perfect right? But Adam and Eve still sinned. What prevents us from sinning in heaven?
I gave this to my "Hard questions" discussion group some time ago and I think we came out with a pretty good answer.
It's a good answer, but not a linear one, so I'll just throw stuff out there.

1 Nowhere in Genesis does it say that Man was complete, or even perfect.
2 When God made man and put the 'breath of life' in him, it was the same thing as animals, it just meant that he responded to external stimuli (alive).
3 Although I don't see evidence for this, most people I've run into think that we weren't around in the garden very long - less than a week.
4 Man was made in the image of God, but so are we. An image is just a picture, it's not as strong as the real thing. (like nature is in the image of God, but it's not obviously infinite)

I'm thinking that God is still 'making' us, in the sense that he's sanctifying and educating us in the way of following him. In heaven we will be true sons of God and know how to avoid evil, but not before.

Some stuff to think about:
Galatians 4 describes limitations/rules put on us as heirs of God but not yet sons, and then says that we are now becoming sons of God and do not need rules. We will still follow Gods way, but with the Holy Spirit. We will still try to obey his perfect law, but by understanding why he made those laws etc. ... Anyway. In the same way, our current physical limitations (like not being able to fly) may prevent us from doing too much damage with our errant minds. Later on when we're perfect, God will give us resurrected bodies. Cool!
Random theory: 7 days of creation. Each day is a thousand years. Some estimate a 8k yr old universe, others say 6k. I'm thinking 6k. So what if God is still 'creating' us and history will be 7k years long? That means we have 1k left, maybe that will be taken up by the 1000 years of ruling by Christ? That gives us basically no slack time before JC comes back! - Now, it's just a theory. And we won't know when JC comes back. But it doesn't hurt to expect it any minute.

Anyway, I've got more posts to come, I have to keep these short.