"Apple has recently announced several enhancements to our product lines and we are offering customers the option to select one of our new products. You may change your order or request a return using this web site. Please enter your order and email information below"
Those in the know say your original purchase has to be a) from the Apple retail store or Apple online store and b) within 14 days of when the "enhanced" products are announced. So no way I'm getting a partial refund on that Powerbook I bought in May.
Now that I think about it, this is really just a much more user-friendly version of their existing 14-day return policy, but it's a significant improvement to the process, so it's worth mentioning.