Well known consumer-friendly site, the appropriately named Consumerist, brings the confessions of an anonymous Apple Specialist. While these cover everything Apple sells, from Macs to iPods, they certainly apply to the iPhone.
Top tips? If you can't reset or restore your iPod (or iPhone!), it's done. AppleCare extends your warranty, that's it. .Mac and ProCare may not be worth the cash, but One-to-One is a deal. If your item (and iPhone?) is outside the return date, Apple may take it back if it's still sealed, maybe even if it's not. No insider info on unreleased product. And the email survey is your one way ticket to managerial ear-time.
Of course, your mileage, and your individual Apple Store, may vary, so buyer still beware.