I need to chime in here with a slightly different perspective on paypal and ebay -- I had a pretty positive experience when I was scammed. Obviously I hope that the thread starter gets his macbook, or, at least, that ebay and paypal makes him whole. My advice is to be persistent with them. It may pay off.
Here's what happened to me:
I bought a few iPhones to unlock and sell back in September. My goal was to make just enough money so that I could afford to buy one for myself.
One of the first I posted on ebay was purchased by a guy a Florida who wanted me to ship it to his friend in Vietnam. Of course, in hindsight, there were probably 95 different reasons why this was a scam, but I was greedy and I wanted to sell it. So I ignored them.
I shipped it UPS. I realized that I might be getting scammed when the buyer left positive feedback for me before his "friend in vietnam" received the item. Finally, about a week after I shipped it, paypal placed a hold on the payment and took the money out of my account, alleging that the transaction was unauthorized activity on the buyer's account. Ebay also cancelled the auction, deleted the feedback, and, at least, refunded my selling fees. So apparently, someone had hacked into this guy's ebay and paypal accounts. Because I had shipped to a non-confirmed address, outside of the US, I was ineligible for the paypal seller protection plan or whatever it's called. I thought I was screwed.
I emailed paypal and ebay almost daily. I forwarded them all of the emails from the "buyer". I kept them updated with the status, including my attempts to get UPS to stop delivery and send me back the phone. I gave them the tracking number.
I also sent paypal a polite email asking for all of the relevant facts so that I could determine what my rights were against ebay, paypal, and the account holder under the various agreements and the laws of the relevant states law (my state, Florida, wherever ebay and paypal are headquartered) for possible failure to take adequate steps to protect the integrity of the process. About a week after my email, paypal emailed me and told me the "buyer" had dropped his dispute. I find this hard to believe -- I suspect that they simply didn't want to deal with my email. Of course, I don't know for sure.
I was also successful in getting UPS to get the iPhone back for me, albeit at my own cost (about $175 for expedited shipping from vietnam to the US). I had to call UPS basically everyday for about three weeks to get them to find the package, stop delivery, and send it back to me. When I emailed ebay and paypal, telling them that UPS was sending me back the phone, I got automated responses telling me that the relevant cases/disputes had been finally resolved.
So the bottom line was that I bought an 8GB iPhone for $420 (including tax), sold it for $500, paid paypal a fee of about $40, spent $175 to getting it back from vietnam. So, basically, I got an iPhone for approx. $135. But, it took about a month to get it back from vietnam and way too much of my time. Definitely not worth it.