Why are we here?

I don't think I mean that in the way you might think I do.

I really like that last sentence, just for the sheer 'huh?' factor.

Anyway, this is a question that occurred to me last night, and it's directed primarily at those that believe in both a Creator and some sort of afterlife, with a specific focus on a paradisaical afterlife. The question, more specifically, is:

Why has your Creator deity put us, human beings, on Earth, rather than simply having us be born in [Heaven]? Why have a life, followed by an afterlife, instead of just having the after- and skipping the before-?

Removing all the religious aspects, the answer from an atheistic perspective is very simple; we live on Earth because Earth formed in an appropriate area around an appropriate star out of appropriate ratios of elements that then came together to form self-replicating molecular structures which then, over time, became more and more complex, eventually resulting in us. We're not in Heaven because there is no Heaven; this is all we get. It doesn't sound all that simple, but in essence all it means is that we're here because 'here' is capable of supporting us.

This question, for me, is kind of half-and-half. On the one hand, I see it as the kind of question that many atheists throw at the religious, trying to convince them of the errors in their logic (this isn't typically a tactic of mine, but I see it used all the time). On the other hand, part of me is genuinely curious. Why muck about being mortal when we could just come into being in spirit forms in Heaven? What's the reasoning there, for whatever religion you happen to subscribe to?