Hi mgrumo,
I'm so sorry to hear that this has happened to you. Although I think we can all understand your disappointment and frustration with eBay's Buyer Protection program right now, it doesn't solve your problem, which is trying to locate your package.
I had a similar thing happen to me, though it was not a package per se that was misdelivered. It turns out that there is a house number that is the same as ours, only it is one street away, so it's on the correct route, just put into the wrong box. We were fortunate in that the neighbor (who we don't know) put a post-it note on it telling the mailperson that it was delivered to the wrong address. I can't help but wonder if a similar thing has happened in your situation. Perhaps you can persuade the Postmaster to take another deeper look into your situation.
Also, if someone stole your mail, then this is a federal crime and the Post Office has inspectors who should be able to look into this. If the mail was misdirected, misdelivered, or whatever they want to call this, they should have an investigator look into it. You may also want to to with your local police department. They may be able to assist you in some way.
I found some information that could help you at the USPS web site, but the format for the links is too long for this post. I couldn't get past the preview page to post them. so here is a link to the Frequently Asked Questions page. From there I clicked on Receiving Mail, and then Track Mail, Confirm Delivery, and Report Missing Mailpieces (Domestic)
http://faq.usps.com/eCustomer/iq/usps/request.do?create=kb:USPSFAQ
Click on Report Missing Item once you get to the correct page.
Good luck and I hope you get your item soon! 