One of the reasons why I'm cynical about ebay accepting bitcoin is because it seems to me like a direct competitor to paypal. How will they implement it and how will they provide buyer protection? It just seems the opposite of what PP is about. Hope I'm wrong though.
I could think of one way. They would just have to either create their own payment processor or escrow system like bitpay or whatever or integrate it into paypal somehow. Ie you pay for the item and the funds go into ebay/paypal's bitcoin escrow. Once the buyer has recieved the item the funds are released. If they don't get the goods the funds will probably get sent back. I'm sure they'd have to do something like thos rather than work with an external compant.