OpenBazaar is a great concept, and from the moment I learned of bitcoin, I kept wanting to build something like this myself (though sadly I never got around to it).

I think the beauty of the idea is that since it's decentralized by nature, anyone can build their own 'eBay' site/app to list the many products/services available throughout OpenBazaar.  It would be like if eBay was open source and you didn't have to ever go to 'ebay.com' to buy/sell anything.  I think early on this sort of concept would be best opened to developers to build applications/sites through which the later wave of public users could actually use.  At this stage, it's too early for wide usage.

The major flaw though is that there is no incentive for arbitrators because there are no fees.  And because there are no incentives for arbitrators, there will be a lot of scams abound ... or you'll have to rely on building trust over time; trustworthy buyers and repeat customers.  So, I don't see this turning into eBay per se, but more of a decentralized e-commerce platform for shops, though still, it can easily become scam central.

Really, in the end, unfortunately it will work best for dark markets, which may in effect possibly drive up bitcoin transactions more than legal markets.  Regardless of how much the OpenBazaar team claims to be against the sale of illegal goods/services, this platform will be best used for that purpose.

For it to work well for legal goods/services, there would have to be a fee structure with incentives for arbitrators/escrow services.