If you're a beginner, watching the TdF peloton for an idea of how you should be riding may not be the best idea. A little more upright is fine, and that's how most of those guys start out in training every year anyway. There's a wide variety of very effective positions anyway - Lance is famous for his hump-backed slouch, Lemond for his long reach and horizontal back. On the other hand, Andy Hampstead had a more upright style and an excellent posture, and Sean Kelly always seemed to be up half a head above the group, keeping an eye on things.

I usually gauge my own fit by how effectively I can use a variety of riding styles and positions - over the course of many miles, you need more than one.