They are an escrow service. I was thinking about selling on ebay but didnt have the balls to do it. Basically with bitcoins there is no proof that the buyer received the coins since they arent delivered conventionally, ie the mail. Through the mail their is tracking and what not to prove delivery. Use these guys and it acts as a proof of receipt.
Unfortunately this is a bad idea. Lack of escrow is not the problem. Payment reversals due to Paypal disputes is the problem. This can happen well after escrow has closed. The ONLY thing that can potentially help you as a seller is the mailing of a tangible item to the buyer's verified Paypal address. There is no way Paypal will possibly side with you on a dispute if you don't have evidence of that shipment. Again, Paypal will not even consider your case if you don't have proof of mailing a tangible good to a verified address.